This research aimed to improve student’s science processes skill by problem based learning on sub topic water pollution in state junior high school 1 Sumberrejo Bojonegoro. The purpose of this research is to describe the feasibility of problem based learning, describing improvement student’s science processes skills, describe the improvement of student’s learning outcomes, and the student’s response to the problem based learning model. The method of the research is Pre Experimental Design. Students of class VII B State Junior High School 1 Sumberrejo are the subject of this research. The result of feasibility of problem based learning model is 3,65 which is good. Mastery learning classically of student’s science processes skill improve from 10% in pre-test, 46% in post-test of the first meeting, and finally 88% in post-test of second meeting, improving student’s cognitif outcome with analyze of uji t resulting t calculation (11,4) > t tabel (1,69) which can be concluded that there is significant result between pre-test and post-test, improving student’s psycomotor outcome by mastery learning classically 100% and student’s affective outcome by mastery learning classically 81% and student’s response of problem based learning model is 93,75 %. It is concluded that through problem based learnig model can improve student’s science processes skill and student’s learning outcomes. Keywords: Problem based learning, Science Process Skills, Learning outcome, Sub topic of water pollution.