This experimental study was aimed at analysing the effects of Think-Pair- Share (TPS) cooperative learning on students reasoning ability and mathematical problem solving. The population of this study was all students of Islamic Junior High Schools (MTs) of the 2012/2013 academic year in Tasikmalaya; while.the randomly taken sample was students of MTs Nurul Falah. Two classes were choosen, one class (VIIB) was assigned as experimental class and class VIII-C as control class. The instrument used was test on mathematical reasoning and problem solving ability. Data was analyzed using two different average test and ANOVA.The results showed that: (1) the improvement of student's reasoning and problem-solving abilities treated through TPS Cooperative Learning was better than those treated through conventional model, (2) there were improvement differences of reasoning and mathematical problem solving abilities in both classes, in terms of high, medium, and low level capabilities, and (3) there was interaction between learning and mathematical prior knowledge of students group (high, medium, low) in reasoning ability and mathematical problem solving. There was also revealed that there was a contribution for each phase of the TPS Cooperative Learning on student'learning.