Formative assessment as an integrated process in teaching and learning process is highly important especially in assessing speaking skill. Thus, maintaining the characterstic of formative assesment in teaching and earning process is vital so that the assessment is more structured and meaningful. This research was aimed to know students’ perception of formative assessment on speaking skill and to find out whether or not there is a correlation between their perception of formative assessment and their achievement in speaking class. Total sampling was chosen since there was only 73 respondents. The subject of this research involved all of the third semester students in English Education Department of Universitas Muhammadiyah Purwokerto. The result of questionnaire data analysis shows that 88% students have positive perception toward formative assessment which shows 3,6 point of five-point Likert Scale. Meanwhile, the analysis using Perason Product Moment Correlation shows r value of 0,066 meaning that the correlation between students’ perception of formative assessment on speaking skill and their achievement in speaking class is very low and not significant.