The purpose of the study was to examine effects of web-based PBL on problem-solving skill and motivation of learners. In order to achieve the purpose, it was hypothesized that web-based PBL would be better to develop the problem-solving skill and motivation than traditional instruction using printed materials. In the study, 75 elementary students were randomly assigned to the experimental groups, web-based PBL and traditional instruction. Instructional materials were developed for two groups respectively about 'Natural environment and living in the country', which is the first chapter of social study for fifth grade. An experiment was executed in the regular class hour for 80 minutes approximately. Based on the results obtained from the experiment, it was found that web-based PBL was more effective in devoloping problem-solving skill and motivation of learners than traditional instruction. In conclusion, web-based PBL was suggested to be used in order to facilitate problem-solving skill.