Although writing and translation are closely related text productions, their interface has rarely been studied in translator training. This study examined student translators' writing and translation products in terms of their quality, errors and self-perceived mental workload. Data were collected from 11 intermediate-level translation students at a university in mainland China. They were asked to complete four tasks: L1 (Chinese) writing (L1W), L1 (English-Chinese) translation (L1T), L2 (English) writing (L2W), and L2 (Chinese-English) translation (L2T). The results of quantitative analyses revealed no significant linear correlation between self-perceived mental workload and quality/errors, but a significant effect of task type on mental workload. Errors most frequently occurred in translation and L2 text production. The L2W error rate predicted L2T scores and L2T error rates. A discrepancy was noted between the students' self-evaluation and their actual performance. The findings of this study may help researchers and teachers gain a fine-grained understanding of students' performance in writing and translation and shed light on the development of pedagogical measures in translator training.