the objective of this research were to 1) develop a computer assisted Instruction (CAI) on the computer system, 2) efficiency validation of the developed CAI and, 3) compare the student's achievement before and after using the developed CAI by using STAD technique on the computer and information technology subject in information technology department at loei technical college in academic year 1/2013. The tools for this research were CAI that consisted of the content with 3 units, pretest, exercise, and posttest. In experimental procedure, the sampling started with tested the pretest, study the CAI , and did the posttest. The data were analyzed by mean and t-test for testing the hypothesis.