SUMMARY
The aimed that wants to be achieved in this research are: 1) Developing accountancy learning materials using inquiry basis to increase the critical thinking and learning achievement of students; 2) Knowing the effectiveness of accountancy learning materials using inquiry basis to increase the critical thinking and learning achievement of students.This research uses the research and development menthod from Borg and Gall. This research develops the accounting learning material using inquiry basis.The subject in this research Is the students of SMK N 1 of 11 Accounting. The learning materials developed have been validated by 4 validator. They are : 1) the language expert, 2) media expert, 3) material expert, 4) practitioner. The significant test uses post test only control design Model.The result of the research is as follow: 1) The result of the research is the accounting learning materials with inquiry basis. The learning materials which are developed are presented by using thr case that must be finished by the students based on the Inquiry basis learning scenario with the steps started by setting the hypothesis, making the experiment, collecting the data, analyzing the data, and making the conclusion. After doing the development, the validation to the learning materials is done. The result of validation shows 87,96% which means the learning materials developed are valid and they can be used to try out, 2) The product developed is proved to be significant to improve the ability of critical thinking and learning achievement. The result of try out shows the average score for the experiment class is 81,85 and the average score for control class is 71,97. The average score shows that the experiment class has higher score that the control class. Next to test the signification product, it is done by using t-test. The result of t-test shows that the significant score 0,0 or <0,05 means that H0 is refused and Ha is accepted. This shows that the development of inquiry basis accounting learning materials are proved significantly effective to improve the ability of critical thinking and the students' achievement.