The Objectives of this research were:  1) to develop Web-based instruction 2) to find the efficiency of Web-based instruction 3) to compare the students’ learning achievement before and after learning with Web-based instruction. 4) to develop the students’ computational thinking skills and 5) to study the students' satisfaction towards using Web-based instruction. The Sample group, selected using Simple Random Sampling by drawing out 1 classroom, was 34 students of Rajavinit Mathayom school, studying computational science in the 2nd semester of academic year 2019. The research instrument consisted of Web-based Instruction, lesson quality evaluation form, pre-test/post-test, computational thinking skills evaluation form, and satisfaction evaluation form. 
    The finding indicated that the efficiency of the web-based Instruction was 83.82/80.15, the average of post-test score was higher than the average of pre – test score at a statistical significance level .05. The students’ computational thinking skills was in a very good level (82.66%) and the assessment showed a high level of the learners’ satisfaction