The purpose of this study was to explore the effect of visually assisted guided discovery learning strategy on grade 10 students' problem solving skills of learning plane geometry in Woldia City, North Wollo, and Ethiopia. A nonequivalent quasi-experimental pretest-posttest-control group design and a case study design were used. The population of the study constituted 96 students assigned into three groups: experimental group-1 (n=29), experimental group-2 (n=39) and comparison group (n=28). Three secondary schools were purposefully selected and assigned to experimental and control groups by simple random sampling method. Data were obtained from pre-test and post-test of plane geometry problem solving skill test results and from student semi-structured interviews were conducted, verified and used for the study. Quantitative data were analyzed using paired sample t-test and one-way ANCOVA, and qualitative data were analyzed using case description reports. The difference was statistically significant with large effect size. Furthermore, the one-way ANCOVA after visually assisted guided discovery teaching strategy showed a significant effect on student scores. A detailed interview analysis of the data revealed that using the visually assisted guided discovery teaching strategy can improve students' problem solving skill in learning geometry and students' ability to employ the problem solving strategy is developed.