This qualitative research aim a) investigating the kind of vocabulary error omitted in students’ speaking performance. b). investigating the source of error on students’ speaking performance. The study used observation checklist and interview guide to gain type and source of error omitted by the students in performing a descriptive text. The sample of the study were 30 students in VII A1 grade students of SMP Negeri 4 Singaraja in academic year 2019/2020 through purposive sampling. The data were collected using four stages in procedure of data collection. The result showed 24 from 30 students omitted vocabulary error. There are 42.86% omission error, 25.71% addition error, 17.14% misformation error, and 14.29% misordering error with interlingual source of error 39.13% and intralingual source error 60.87%.
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