The purposes of this study were 1) to develop an instructional model integrating WebQuest Learning Approach and Reflective Practice to enhance English critical reading ability of undergraduate students, 2) to investigate the effectiveness of the instructional, and 3) to investigate undergraduate students? English critical reading ability development learning with the instructional model. The research and development processes were divided into four phases: 1) studying of the significance of the problem and learning approaches, 2) developing of the instructional model integrating WebQuest Learning Approach and Reflective Practice, 3) Studying the effectiveness of the instructional model integrating WebQuest Learning Approach and Reflective Practice, and 4) Revising and developing the instructional model integrating WebQuest Learning Approach and Reflective Practice. The sample consisted of 11 second-year undergraduate students majoring in English as a foreign language at the Faculty of Language, Arts, and Humanities in a university in Cambodia. The sample were purposively selected and studied with the newly developed instructional model for 10 weeks, total of 30 hours. The instrument was the English critical reading ability test. Quantitative statistic used in this study was Wilcoxon Signed-ranks test. Qualitative data were analyzed using content analysis. The results showed that: 1. The instructional model integrating WebQuest Learning Approach and Reflective Practice consisted of five learning steps: 1) Generating skepticism, 2) Assigning the Quest, 3) Exploring the Quest, 4) Reflecting the Quest and 5) Concluding the Quest. 2. A Wilcoxon Signed-Ranks test indicated the sample (were taught with the instructional model integrating WebQuest Learning Approach and Reflective Practice) had significantly higher critical reading ability mean score in the posttest compared to those in the pretest at .05 level of significance. 3. The sample (were taught with the instructional model integrating WebQuest Learning Approach and Reflective Practice) resulted in the higher development of the English critical reading ability after experienced with the instruction.