This research aims to determine the difference science process skills of students before and after learning by using of guided inquiry model and how much influence guided inquiry model of the science process skills class XI SMA Negeri 3 Singkawang. The method used is pre-experimental design with the design of one-group pretest-posttest design. The sample in this study were students of class XI IPA 2 that was determined by random sampling techniques. Data collection tool that used is the science process skills test in the form of essays and interview guidelines. Based on the results of data processing the results of pretest and posttest by using the Wilcoxon test, obtained Asymp.Sig (2-tailed) of 0.000 <0.05 (less than 0.05) so that Ho is rejected, which shows there is differences in science process skills of students before and after learning by using of guided inquiry model. The results of calculation of Effect Size (ES) obtained value of 2.12, that showed guided inquiry model provided the effect of 48.30% on improving students\u27 science process skills
