This study investigated the effects of problem-solving method of teaching on secondary school students' achievement and retention in Social Studies. The study adopted the quasi-experimental, pre-test, post-test, control group design. The sample for the study consisted of 240 Junior Secondary School Class II students randomly selected from six secondary schools in Ekiti State, Nigeria. The instrument used for the study is the Social Studies Achievement Test (SSAT) designed and validated by the researcher. Section A of the instrument consisted of the bio-data of the respondents while section B was made up of 40 multiple-choice items designed to measure the students' achievement and retention in Social Studies. Four hypotheses were raised and tested at 0.05 level of significance. The data were analyzed using t-test and ANCOVA statistical tools. The results showed that there is a significant difference between the achievement mean scores of students in the experimental and control groups. There is a significant difference between the pre-test mean scores and achievement mean scores of students in the experimental and control groups. There is a significant difference between the retention mean scores of students in the experimental and control groups. There is a significant difference between the achievement mean scores and the retention mean scores of students in the experimental and control groups. It was discovered in the study that problem-solving method is more effective than conventional lecture method in improving students' achievement in Social Studies. It was therefore recommended that teachers should be innovative in handling their lessons by relating them to the day-to-day life of students in such a way that the students will be challenged to put the lessons to practice as much as possible. Government should also emphasize the use of problem-solving method to teach Social Studies in secondary schools. (Contains 5 tables.)