This study aims to: (1) determine the characteristics of mathematics learning Group Investigation model with scientific approach, (2) develop a valid learning device, (3) test the practicality, and (4) test the effectiveness.The study refers to the model development Plomp: (1) Preliminary Investigation, (2) design, (3) realization, (4) testing, evaluation, and revision.First prototype validated and revised according to input into second prototype.  Validator then tested in a trial class. Device trials conducted in elementary school in V grade.The data is taken from sheet validation, observations, questionnaires, tests, and processed withthe thoroughness of testing, test regression effect, comparisons, test of  the improvement of  problem solving ability. The results showed: (1) syllabus score of 4,28; lesson plan 4,41; student worksheet 4,09; student book 4,52; problem solving ability test  4,16 in the range of 1-5 showed that it was already categorized valid, (2) the effectiveness of the implementation of learning characterized by :(a) learners who value the problem solving more than 75 (minimum thoroughness criteria) reached 95.8%,(b) self-reliance and activity of 89.6% effect on the ability of solving problem(c) the average problem solving ability of Group Investigation Sainitific Approach class was 85,70 greater than the control class was 63,11,and (d) problem solving ability of students in Group Investigation Saintific Approach class increased 61,8%.