The purpose of this research was to identify the common errors made in English writing by Malaysian Chinese primary year 6 ESL students and to determine the extent of the influence of the first language, Mandarin in ESL writing. The Mandarin language uses a logographic writing system while the English language is written in alphabetic scripts. The difference between the two language systems makes it challenging for Chinese ESL learners to master the English language. In this study, which employed a qualitative approach, 15 ESL students from primary year six were chosen as participants for the writing tasks which formed the first part of the study. Completed writing tasks of ten participants were chosen for analysis. Interviews were conducted with three participants to obtain their perceptions on their grammar proficiency. The highest and most prominent grammar errors revealed in the analysis were in the area of tenses, object pronouns, plurals, auxiliary verbs, prepositions and articles. These errors were found to be caused by the influence of the mother tongue through direct translation from the Mandarin language. To conclude, errors are inevitable but they are crucial for ESL learners to make progression in their English writing skill. The results obtained in this study serve as vital knowledge and information for ESL educators to enhance ESL learners' grammar accuracy in writing.