Sio (also spelled Siâ) is anAustronesian language spoken by about 3,500 people on the north coast of theHuon Peninsula inMorobe Province,Papua New Guinea. According to Harding and Clark (1994), Sio speakers lived in a single village on a small offshore island until thePacific War, after which they established four villages on the nearby coast: Lambutina, Basakalo, Laelo, and Balambu. Nambariwa, another coastal village a few miles to the east, is also Sio-speaking.

Michael Stolz (died 1931) of the German LutheranNeuendettelsauer Mission arrived in 1910, and Sio villagers converted en masse in 1919. "Since then the Sio have produced many Lutheran evangelists, lay mission workers, teachers, and churchmen" (Harding and Clark 1994: 31). However, the Sio villages were assigned to the mostly PapuanKâte language circuit, rather than to the mostly AustronesianJabêm language circuit. The first Sio orthography was based on that of Kâte, and was used in the publication in 1953 ofMiti Kanaŋo, a book containing Bible stories, Luther's Small Catechism, and 160 hymns, all in the Sio language. Stolz was the principal translator, although many of the hymns were composed by native speakers of Sio, and the whole volume was edited by L. Wagner, Stolz's successor.

The low back vowel is pronounced[ɔ]. All vowels vary in length, but length is rarely contrastive. Monosyllabic nouns and adjectives tend to be lengthened more than monosyllabic verbs, adverbs, or prepositions. Word stress generally falls on the penultimate syllable.

When Stephen and Dawn Clark ofSIL International began to work with Sio speakers in 1985, the latter expressed a desire to revise their orthography to make it more similar to what people had become familiar with inTok Pisin andEnglish. The eventual results are tabulated in the following chart. The community at first resisted writing the labialized consonants as digraphs, since they clearly regarded them as unitphonemes. They insisted on writing the labialization as superscripts rather than as separate segments. However, by 1992, after many materials were produced in the new orthography, Sio teachers and church circuit officers approved writing the indicator of labialization on the same line, thus acceptingmw instead ofmʷ (Clark 1993).

The first orthography of Sio was devised by the missionary Michael Stolz, based on that of theKâte language, which the German Lutheran mission used as a church and schoollingua franca among speakers ofPapuan languages. (Sio appears to have been assigned to the wrong language circuit.) The linguistOtto Dempwolff served as mentor and adviser to all the German missionaries in New Guinea on language questions. After Stolz died, Dempwolff analyzed his language materials and compiled a short sketch (1936). His analysis differs in several key respects from that of Clark (1993), who has had firsthand experience with the language. The most striking difference pertains to thelabiovelars, which Dempwolff analyzed as coarticulated[k͡p],[ɡ͡b],[mɡ͡b],[ŋ͡m], but which Clark finds to belabialized labials (rounded on release)[pʷ],[bʷ],[mbʷ],[mʷ]. (The letterɋ in the table below here stands for a curlyq with hooked serifs that cannot properly be rendered online.) But Clark also found thatg-[ɡ] and-c-[ɣ] were positional variants of the same phoneme; that trilled[r] is just a conditioned variant of flapped[ɾ]; and that the approximants are conditioned variants of their corresponding vowels.

• Clark, Dawn S. (1993). "The phonology of the Sio language."[1] In John M. Clifton (ed.), Phonologies of Austronesian languages 2, 25-70. Data Papers on Papua New Guinea Languages, 40. Ukarumpa: Summer Institute of Linguistics.
• Dempwolff, Otto (1936). Bemerkungen über die Siâ-Sprache. Zu den Aufzeichnungen von Missionar Michael Stolz. (Copied out by L. Wagner, 15/7/1936.) Ms. 13 pp.
• Harding, Thomas G., and Stephen A. Clark (1994). The Sio story of Male.Pacific Studies 17, no. 4, 29-51.
• Stolz, M., trans.; Wagner, H., ed. (1953). Miti Kanaŋo: Siŋga Wa Waseki Wa. Madang: Lutheran Mission Press.

• Paradisec has two collections ofArthur Cappell's materials (AC1,AC2) and one collection of Malcolm Ross's materials (MR1) that include Sio language materials.
• The New Testament and Psalms in the Sio Language of Papua New Guinea

• Ngero–Vitiaz languages
• Languages of Morobe Province

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• Language articles citing Ethnologue 18
• Articles with short description
• Short description is different from Wikidata
• Language articles with old Ethnologue 18 speaker data
• Articles containing Sio-language text
• Pages with plain IPA