This study aims to find out the types of errors and to analyze the syntactic errors committed by third-semester students of the English Education Study Program at Mahasaraswati University Denpasar. This study is classified into a qualitative research design. To analyze the data, theory types of errors proposed by Dulay et al. (1982) and sources of error from Richards (1974) were applied. The data were sentences on argumentative essay writing containing errors taken from final assignments of the third-semester students of the English Education Study Program at Mahasaraswati Denpasar University. There are 25 data containing omission, 5 data containing addition, 35 data containing misformation, and 1 data containing misordering. Meanwhile, the sources of syntactic error that the researchers found are 12 errors caused by interlingual transfer and 33 caused by the intralingual transfer.