Covariational reasoning plays significant role for solving problems. This study examines the covariational reasoning of postgraduate students when solving mathematical problems such as fraction, velocity and acceleration, proportion, and integral. 26 postgraduate students of mathematics education, universitas negeri surabaya, are involved in this study. Generally, mental action of students more prominent on fraction and proportion than on the other issues. On fraction and proportion problems, all students are able to fulfill all mental actions such as coordinating the value, the direction, and the amount of change of one variable, and also coordinating the average and the instantaneous rate of change of the function. However, on velocity, acceleration, and integral problems students can not show their mental actions well. The shape of their graph are irrespective with initial point, so that they only fulfill 3 of 5 mental actions in covariational reasoning. These findings suggest that learning in mathematics should place increased emphasis on problem involving graph to promote covariational reasoning of the students.