Critical thinking is an active and organized cognitive process which intends to understand the individual himself/herself, the events, situations and thoughts around him/ her by taking into consideration the individual and the thoughts of others that he/she interacts with. For this cognitive process, it is vitally important to be willing. Because of the need for a valid and reliable scale to measure critical thinking disposition especially in secondary education, the present study conducted aims to determine the validity and reliability of UF/EMI (University of Florida Engagement, Maturity and Innovativeness) Critical Thinking Disposition Instrument in Turkey conditions. The five-point Likert Scale composed of 26 items was applied to 342 Grade 9 and Grade 10 students. In order to analyse the triple factorial structure of the scale, confirmatory factor analysis (CFA) was carried out. As a result of analysis, one item was excluded from the scale. The obtained results indicated that 25-item scale resulting in three factors is consistent and compatible with the data. For the reliability of the scale, internal consistency coefficients of the entire scale and its sub-dimensions were checked out. The obtained Cronbach's Alpha internal consistency coefficient is 0,91 for the entire scale, 0,88 for engagement sub-dimension, 0,70 for cognitive maturity sub-dimension and 0,73 for innovativeness sub-dimension.