English is spreading all over the world and it is still the prominent international language. Its developing will be influenced by the local language. One of the local languages in Indonesia is Javanesse. Javanesse has so many variant or dialect. One of them is Ngapak Javanesse. Ngapak Javanesse belongs to the native of Banyumas, Banjarnegara, Cilacap, Brebes, Tegal, and Western Kebumen. It is interesting to investigate whether students’ first language (Ngapak) affects their language performance at campus and whether sociolinguistic aspects such as language choice and attitude contribute to their oral and written language competence. A research to see the effect of first language to children’s oral and written language competence is conducted to 45 English Education Department Students in IAIN Purwokerto. Oral and written tests are conducted; the statistical analysis of the data obtained then are related to the first language of the students and to their language behavior. The research shows that there is students’ first language affects their English language performance both in oral and written form. Students who come from urban area has better oral and written English language performance. The research also tells us that students has different language behaviour based on first language, gender, age, and motivation. Students who use Ngapak language as the first language speak English more in Ngapak style. Female students use English better than male students in all domains. Older female students have more language awareness than the younger and all male students. The motivated students have better English performance. Code mixing and code switching also occur in most native students of Ngapak.