The study assessed the effects of Activity-Based and Problem-Solving methods on students' academic performance in Basic Science in Junior Secondary Schools in Kaduna State, Nigeria. The study was carried out with Seven objectives: determine the Pre-test and Post-test performances of students taught Basic Science using Activity-Based and those taught using Problem-solving method; determine the performance of students taught Basic Science using Activity-Based and Conventional method; examine the effect of Problem-Solving and Conventional method on the performance of students in Basic Science in Junior Secondary schools in Kaduna State, Nigeria amongst others. The study adopted quasi experimental research design. The target population of the study was made up of 119, 238 Junior Secondary 2 Students in Kaduna State, of Nigeria. The sample size for this study consisted of 3 intact classes of 218 Junior Secondary School students. Purposive sampling techniques was used to choose the sample size. The instrument used for data collection in the study was adopted test of multiple choice in Basic Science Junior Secondary Certificate Examination, 2010-2014. The validated instrument was pilot tested and a reliability coefficient of 0.79 was obtained. The statistical tools used for data analysis included descriptive statistics mainly mean and standard deviation which was used to respond to the research questions raised in the study. The t-test was used to test hypotheses 1, 2, 3, 4 and 5, and two-way Analysis of Variance (ANOVA) was used to test hypotheses 6 and 7. The hypotheses formulated for this study were retained or rejected at 0.05 level of significance. The study established among others that, Students taught basic science using activity-based method had a higher mean score and performed significantly better in the post-test (P-value .002 <0.05), Students taught basic science using Problem-Solving method had a higher mean score and performed significantly better in the post-test (P-value .002 <0.05). The post-test mean performance of students taught Basic Science using Activity-Based method is slightly higher than the post-test mean performance of students taught Basic Science using Problem-Solving method (pvalue .004 O.05) Students taught basic science using activity-based method had a higher mean score and performed significantly better than their counterparts taught using conventional method (P-value .0030.05). It was concluded that the activity-based method was more effective to teach Basic Science as the method enabled students to achieve higher mean score and performed better than their counterparts taught using both problem-solving and conventional methods. Recommendations were that; Teachers and school Managers, should provide and encourage the use of both Activity-based and Problem-solving methods as they both have been proved to be effective empirically in enhancing students' academic performance; Basic science teachers should be encouraged to use Activity based method because of its positive effect in enhancing students' academic performance; and Teachers should be encouraged to make their classrooms active learning classrooms by ensuring that their students are exposed to meaningful Problem-solving activities that will make them active learners not passive listeners or receivers.