In recent years, peer assessment has been increasingly used as an alternative method of assessment in classrooms. The study described in this paper employed a 13-item Likert-scale instrument to evaluate participants' attitudes towards both general (seven items) and online peer assessment (six items). A sample of 280 pre-service teachers and 108 in-service teachers from northern Taiwan participated in the study. A difference in attitude was found between pre-service and in-service teachers, because the latter viewed peer assessment as a learning aid. Our results also showed that male pre-service teachers had more positive attitudes towards peer assessment in general; male in-service teachers also liked the online approach more than did their female counterparts. Item-by-item analyses have been conducted in order to explore both the differences in attitude between pre-service and in-service teachers and to identify any gender effects.