This research aims to determine the effect of portfolio assessment methods in teaching on the learning motivation and learning achievement of social study. This research was the experimental research of the post-test only control group design. The sample was 40 students of class VI. Learning motivation questionnaire and learning achievement test were used to measure achievement motivation and social study achievement of students. Data were analyzed by using one-way Manova. The results show that: (1) there is a significant difference in motivation between students who took the student learning portfolio assessment method and students who took conventional methods of assessment, (Fobs=166.58, p<0,05), the average score of learning motivation of students who take learning portfolio assessment method of 103.92 is greater than the average score of the learning of students who take conventional assessment methods of 75.28; (2) there is a significant difference in academic achievement between students who took the student learning portfolio assessment method and students who took conventional methods of assessment, (Fobs=81.145, p<0,05), the average score of learning achievement of students who take learning portfolio assessment method of 32,00 is greater than the average score of the learning of students who take conventional assessment methods of 25.78; (3) simultaneously, there are differences in motivation and achievement of significant learning among students who took the process of learning to use the portfolio assessment method and conventional assessment methods (Fobs=141.341, p<0,05).