The article is devoted to the experimental research of efficiency of solving psychodiagnostic tasks by the students-psychologists with different thinking styles. In the theoretical part a style of thinking as a determinant of successfulness is concerned. The hypothesis is the supposition that efficiency and ways of diagnostic tasks made by the students-psychologists are determined by a dominating thinking style. For the examination of the hypothesis the following methods were used: questionnaire “Styles of thinking” by Brams Harrison, the method of experiment (solution of 6 tasks from real consultative practice), content-analysis of protocols and correlation analysis by Ch. Spirman. The research has been done during some years with students of 4 and 5 courses in South-Russian Humanitarian Institute. The results are the following. Students-analysts are rather successful. They demonstrate good diagnostic process, put forward adequate hypothesis and choose adequate methods, but they don’t formulate recommendations. For the students-realists it is important to render support to the client and give feedback. The quality analysis showed that they are inclined to individual forms of work. Pragmatics are characterized by chaotic behavior, they don’t put forward hypotheses, offer standard methods. Idealists are the worst. They have difficulties in logics and formulating questions to the client. Synthetics on the whole display insufficient success, but they can solve the task correctly due to guessing or hypotheses. Synthetics operate with the methods poorly. Experimental data demonstrate that the thinking style often defines diagnostic search; variety and quality of put forward hypotheses, adequacy of choosing methods of research.