The study aimed to discuss the impact of project-based learning on primary fifth graders with regards to inclination of self-regulation learning readiness and critical thinking disposition. The study adopted the Solomon four-group design with study objects taken from fifth graders from specific primary school in Kaohsiung. A total of 4 classes were randomly sampled with 2 classes being the experimental groups and 2 classes being the control group. The experimental group was applied with the six steps from WebQuest(Dodge & March,1995) as Scaffolding project-based learning in ¡§Taiwanese traditional Arts and Culture,¡¨ where the control group is excluded. After conducting 24 classes of experimental teaching for 6 weeks with 4 classes per week, t-test and two-way ANOVA were applied to understand the enhancement effect of self-regulation learning readiness and critical thinking disposition on fifth graders accepting project-based learning. The study further comprehend the impact of implementation of project-based learning for the self-regulation learning readiness and critical thinking disposition of primary school fifth graders with low, intermediate and high academic achievement. The research results are listed as follow: I. Under ¡§Unprecedented conditions,¡¨ the project-based learning program facilitates self-regulation learning readiness of primary fifth graders. II. The implementation of project-based learning can improve self-regulation learning readiness of primary school fifth graders with intermediate and high academic achievement. Students with high academic achievement show higher statistical significance than students with intermediate and low academic achievement with regards to improvement on self-regulation learning readiness. Students with intermediate achievement with regards to progress in self-regulation learning readiness do not show significance higher than students with low academic achievement. III. Project-based learning facilitates improvement on the critical thinking disposition of primary fifth graders. IV. Project-based learning can improve the critical thinking disposition of primary fifth graders with high academic achievement. The students with high academic achievement show higher significance than students with intermediate and low academic achievement with regards to enhancement of critical thinking disposition. Students with intermediate academic achievement do not show significance higher than students with low academic achievement with regards to progress in critical thinking disposition. The following recommendations are proposed according to the study results for curriculum teaching and future study: I. Implement the advantages of WebQuest to design project-based learning and to increase the number of classes. II. Students with different level of capacity will undergo different layers of project-based learning, which will be implemented to teaching with theory of cooperative learning. III. Researches undergo long-term follow-up or gradual removal of the scaffolding may be used to increase qualitative data collection and analysis.