The purpose of the present paper was to investigate the effect of Student Teams Achievement Divisions (STAD) method on Problem Solving Ability in relation to Critical Thinking. A Sample of 180 (90 Experimental group and 90 Control group) students of 11th class was taken from Government Senior secondary Schools of Ludhiana district of Punjab. The experimental group was taught through Student Teams Achievement Divisions Method for a period of 30 sessions at the rate of 60 minutes per day. On the other hand, control group was taught the same concepts with the help of traditional method for the same period of time at the same rate. Mixed Type Group Test of Intelligence by Mehrotra (2008) was used to match the groups. Problem Solving Ability test by Dubey (2008) and Critical Thinking Scale (developed and standardized by the investigator) was used as tools for data collection. 2X2 ANOVA design was used in the study. The results of the study showed that Problem Solving Ability of the experimental group who taught through STAD was significantly higher than as compared to the control group who taught through traditional teaching method. Further, the critical thinking has a significant effect on the problem solving ability of the students. Significant Interaction was also found between treatment and critical thinking on the problem solving ability.