This study aimed to examine the effect of cooperative problem-solving method on grade nine secondary school students' motivation towards learning algebra. In this study, pretest-posttest non-equivalent group quasi-experimental design was employed. The data were collected from 142 grade ninth students using mathematics motivation questionnaire and analyzed using paired sample t-test, analysis of variance, and analysis of covariance. The result revealed that there was a statistically significant mean difference between groups on intrinsic goal orientation, extrinsic goal orientation, task-value, control of beliefs for learning, self-efficacy, and total motivation of students to learn algebra. Besides, except test anxiety motivation component, students' motivation and its components to learn algebra were affected by the cooperative problem-solving and the problem-solving methods. However, there was no statistically significant mean difference between groups on test anxiety motivation component. Finally, we recommend that further study is needed to examine how students test anxiety can be improved.