This study aimed to analyze the achievement of critical thinking skills of students through

virtual lab assisted learning in preservice teachers of mathematics. The method used is

weak experiment with the design of the study "one group pretest-posttest design". The

research was conducted on the subject for the static fluid level mathematics preservice

teachers university sector in the city of Cirebon academic year 2016/2017. The research

subjects consisted of one class with the number of samples respectively of 23 preservice

teachers of mathematics. The data obtained in this study is data critical thinking skills that

include identifying the relevant issues, defines the subject matter, giving the reasons of the

experiment, using a strategy logically, doing the things done tentatively, summarized by

considering the situation and then decide, answered questions about the facts, report is

based on observations, consider the appropriate procedures, involving a bit of conjecture

based on those events - events and report experimental generalization. Research hypothesis

testing is done by using the t test on the N-gain critical thinking skills after learning to use

the virtual lab. The results of data analysis showed critical thinking skills gain of 0.58

(moderate). From this analysis it can be concluded that learning-based virtual lab for

preservice teachers of mathematics can significantly improve the critical thinking skills of

preservice teachers of mathematics. Besides, in general, the students give a positive

response to learning to use the virtual lab.