The success of new curriculum and assessment initiatives hinges upon teachers' assessment literacy and conceptions of assessment. However, research has shown that many teachers lack assessment literacy due to inadequate assessment preparation in preservice teacher education. Many preservice teachers' reportedly tend to acquire their knowledge of assessment through working with associate teachers during practicum. There is an urgent need to develop preservice teachers' assessment literacy and conceptions of assessment through high quality assessment courses in teacher education programs. This study examined the effects of Problem-based Learning (PBL) approach on the development of preservice teachers' assessment literacy and conceptions of assessment. Data sources include preservice teachers' online surveys and focus group interviews with both preservice teachers and their instructors.