ackground: The Cognitive style is mainly peculiar to theoretical and academic descriptions with bipolar dimensions. These styles are composed of field dependent and field independent ones which are not constant but current. Objective: The present paper aims to clarify the relationship between the cognitive styles and students' performance in writing response and multiple-choice evaluations. Method: The research methodology is applied in its objective and descriptive in data collection. The target population of this study comprised all students of Mahabad Islamic Azad Universit in the academic year of 1387-88. Among them, 280 have been selected by faculty and sex through stratified random sampling. In connection with the cognitive style, EFT, the learning styles questionnaire has been used to collect the required data and for the students' performance measurement in multiple-choice and writing response evaluations the two parallel forms, quadruple response form and writing response form have been employed. Results: The results revealed that there is a positive and direct relationship between field independent cognitive style and the students’ performance in writing response evaluation, but there is no relationship between field dependent cognitive style and the students’ performance in multiple choice evaluations. Also, there is a significant difference between students from such fields as human, basic, agricultural, and technical sciences due to learning styles. Finally there was a positive relationship between the male and female students’ learning styles. Conclusion: Cognitive styles (field independency and field dependency) should be considered while assessing students' academic performance using multiple-choices and writing response tests