This study aimed at comparing the effect of two instructional models, i.e., group investigation (GI) cooperative learning model and conventional instructional model upon learning achievement in chemistry before and after controlling the of student's creativity. This study was an experimental research using Post-Test Only Control Group Design. This population consisted of all Class XI of Science students at SMA Dwijendra Denpasar in the school year 2009/2010. By considering equality of class ability, a couple of equal ability classes were taken at random as the sample. The data were collected with two instruments, i.e., questionnaire and test. The data on student's creativity were collected by a creativity questionaire, and the data of learning achievement were collected by a chemistry learning achievement test. The hypotheses was tested by using one-way ANOVA, one-way ANACOVA, and one-predictor regression analysis. The results of the analysis show that there was a difference in learning achievement in chemistry between the students who were taught with GI type of cooperative learning model and those who were taught with conventional instructional model (FA = 6,441; p < 0,05). After controlling the effect of student's creativity, it was found that there was a difference in learning achievement in chemistry between the students who were taught with GI type of cooperative learning model and those who were taught with conventional instructional model (Fres = 9,322; p < 0,05). Trough one-predictor regression analysis it was found that there was a functional relation between student's creativity and learning achievement in chemistry (R = 0,8995; Freg = 330,500; p < 0,05), and determination coefficient or contribution of student's creativity on learning achievement in chemistry was 80,91 %. In relation to the findings in this study, it can be concluded that GI type of cooperative learning model affected to the learning achievement in chemistry before and after controlling student's creativity. Hence, it can be recommended that the teachers implement GI type of cooperative learning model and consider student's creativity in designing and implementing chemistry instructional programs in the classroom to help the students to improve their learning achievement.