This research was motivated by the low problem-solving ability of students which had an impact on student motivation in learning mathematics. In solving mathematical problems, learning motivation is an essential element that students must have, students who have high learning motivation will be diligent in doing tasks, tenacious and never give up in solving various problems and obstacles. However, students' mathematical problem-solving abilities and student motivation in learning mathematics are still relatively low, one of which is due to the learning model used has not varied so that students are less actively involved in learning. The type of research used in this study is quasi-experimental quantitative research. The quasi-experimental form used is Pretest-posttest Control Group design Pretest-Posttest. The data collection technique used is a problem-solving ability test by presenting 5 questions in the form of essays and student learning motivation questionnaires by presenting 18 points of statements, each question has been validated. The data analysis used is quantitative descriptive analysis, normality test, homogeneity test, t-test and Likert scale test.Results were obtained (1) paired sample t-test in the experimental class and control class respectively obtained Sig  values so that H0 was accepted and H1 was rejected. (2) Independent sample t-test in experimental class and control class  obtained Sig  value so that H0 was rejected and H1 was accepted. Moreover, (3) the results of student motivation analysis were obtained on average by 81% with solid criteria.The conclusions of this study are: (1) There is no difference in students' initial mathematical problem solving ability before learning in experimental and control classes; (2) The mathematical problem-solving ability of students using the Quizizz-assisted STAD learning model is better than students using conventional learning models; (3) There is an influence on student learning motivation using the STAD type cooperative learning model which shows the percentage criteria of 81% of all 5 learning motivation indicators with the category "very strong" owned by students of SMPN 6 Cilegon City. So that the effect of the Student Teams Achievement Division (STAD) type cooperative learning model assisted by Quizizz on students' problem-solving abilities and learning motivation is quite effective compared to conventional learning models.