The aim of this study is to investigate the effect of laboratory activities based on "Predict-Observe-Explain (POE)" method on pre-service science teachers' academic achievement on "Heat and Temperature" subject in Physics Laboratory III. In the study, the quasi-experimental design with pre-test and post-test control group was used.. 44 pre-service science teachers who attended Physics Laboratory 111 course (Experimental group N = 22, Control group N = 22) was participated in the activities. Laboratory instruction based on "Predict-Observation-Explain"(POE) method was applied in experimental group and Verification laboratory method was applied in control group over a period of 12 week (Pilot activities 6 Weeks, Main activities 6 weeks). In the study, a two-stage "Heat and Temperature Achievement Test", worksheets based on POE and Verification laboratory methods have been prepared by the researcher for students. Heat and Temperature Achievement Test was used as data collection tools. "Heat and Temperature Achievement Test" was applied to experimental and control groups as pre-test, post-test and the retention test. Pre-service teachers'answers to Heat and Temperature Achievement Test were classified according to the understanding categories, and each category was scored.The scores of experimental and control groups received by analyzing the answers to Heat and Temperature Achievement Test according to the understanding categories, were compared Wilcoxon Signed Rank Test and Mann-Whitney U Test. In conclusion, it was determined that laboratory activities based on POE method was more effective on pre-service science teachers' understandings of "Heat and Temperature" subject than activities based on Verification method. In the study, it was proposed to investigate effectiveness of teaching materials based on POE method on other science subjects.