The objectives of the present study were: 1) to design a reading strategy instructional model to promote reading comprehension of Thai EFL undergraduates, 2) to develop a reading strategy instructional model to promote reading comprehension of Thai EFL undergraduates, and 3) to implement a reading strategy instructional model to promote reading comprehension of Thai EFL undergraduates. The participants were 27 third year English majors of Sakon Nakhon Rajabhat University. Research instruments included pre-test and post-test, unit summary writings, a questionnaire of students’ perceptions on the reading strategy instruction, and think aloud technique. The quantitative data were analyzed by mean, standard deviation, t-test for data, the qualitative data were analyzed using content analysis. The findings were: 1) The reading strategy instructional model consisted of five components: (1) principles, (2) objectives, (3) contents, (4) six stages of instructional process including Activating background knowledge, Modelling, Reading with strategies, Summarizing knowledge from reading, Knowledge sharing, and Reflecting, and (5) assessment. 2) the effectiveness of the reading instructional model revealed that the efficiency of the RSI model of the developed model are 77.20/80.06, which meet the 75/75 standard. 3) the extent to which the students’ use of reading strategies comprised of (1) the mean scores of students’ reading comprehension from the post-test was higher than of the pre-test with the statistical significance at .01, and (2) the students gradually increased using both cognitive and metacognitive strategies throughout the experiment. 4) the students’ perceptions on reading strategy instruction was at high level.