The study focused on exploring science teachers’ perception of classroom assessment in secondary schools of Bangladesh. A mixed method approach was used to explore science teachers’ perception of classroom assessment by identifying their concept about classroom assessment and how they conduct assessment activities in science classes. A total of thirty teachers (twenty male and ten female) were chosen randomly to collect quantitative data and twelve teachers were chosen purposively for qualitative data collection from six secondary schools in Dhaka. The study used a questionnaire and interview protocols as main sources of data collection. The study revealed that teachers are holding misconceptions about idea of classroom assessment. Majority of the teachers perceive classroom assessment as summative assessment and it should be through oral questioning. Analysis of quantitative and qualitative data exhibited that teachers perceive students should be assessed both lower and higher order learning using different techniques (self-assessment, peer assessment) and modes (oral, written) of assessment and at the same time they believe that it’s difficult to use multiple techniques and modes of assessment in science classrooms. The overall findings of the study suggest that teachers don’t have clear idea about classroom assessment that results in holding conflicting perception about science classroom assessment.