The aim of this study was describing the validity and reliability of critical thinking inventory. The type of study was survey research. The study population was students of junior high schools in the Province of Bali, Indonesia. Samples were drawn by a multistage random sampling technique. In each district, one school was chosen as a sample and in each school, one class VII and one class VIII were selected as samples. The total samples were 531 students consisted of 271 students of class VII and 260 students of class VIII. The numbers of male and female students were 262 and 269 people, respectively. The critical thinking inventory instrument tested consisted of 62 items. The critical thinking inventory data of students were analyzed with the program of SPSS v.16. Data showed that 61 out of 62 items were valid and the reliability of inventory was 0.887.