The purposes of this research study were: 1) to develop the reasonable inquiry-based learning on social cloud model (RIBL on Social Cloud Model) to enhance undergraduate students' critical thinking, and 2) to evaluate the appropriateness of the RIBL on Social Cloud Model. The research methodology was divided into two steps. The first step was to develop the RIBL on Social Cloud Model to enhance undergraduate students' critical thinking and the second step was to evaluate the appropriateness of the RIBL on Social Cloud Model. The samples in this research study consisted of five purposive-selected experts in instructional design, inquiry-based learning, social network, cloud computing and critical thinking. The research instruments included the RIBL on Social Cloud Model to enhance undergraduate students' critical thinking and the appropriateness evaluation form. Data were analyzed using mean (x) and standard deviation (S.D.). The research findings were as follows: 1) the RIBL on Social Cloud Model to enhance undergraduate students' critical thinking consisted of four components: 1.1) analysis of crucial factors, 1.2) preparation before learning, 1.3) reasonable inquiry-based learning on social cloud process, 1.4) measurement and evaluation, and 2) overall, the samples perceived that the RIBL on Social Cloud Model was highly appropriate and applicable to real practice.