The article presents the results of the development and validation of a new questionnaire for diagnosing openness to experience in a person-centered approach. Openness to experience in a person-centered approach is seen as the ability to encounter new experiences, accept the full range of emotions that arise in the process of this encounter, the accompanying ability for self-reflection (awareness) and the ability to show an active life position (responsibility). The list of statements was compiled based on categories reflecting openness to experience in a person-centered approach, identified in a previous qualitative research. For modeling the questionnaire, the method of structural equations (SEM) was used. The study involved a sample of 400 respondents, aged from 16 to 62 years. The five-factor model is accepted as optimal, the questionnaire includes the subscales: “openness to experience” (4 statements), “acceptance of new experience” (6 statements), “understanding of emotions” (4 statements), “acceptance of negative emotions” (4 statements), “acceptance of responsibility” (4 statements). The SEM results obtained for the questionnaire were: χ2/df = 2.5; CFI = 0.919; TLI = 0.905; SRMR = 0.0597; RMSEA = 0.056. The internal consistency measured by Cronbach's α was: for Scale I — 0.794, for Scale II — 0.813, Scale III — 0.649, Scale IV — 0.755, Scale V — 0.819, the Cronbach's α for the full questionnaire — 0.867, MacDonald's ω — 0.867. The calculation of discriminativity by Ferguson’s method with the Hankins correction gave the following values: Scale I — 0.97, Scale II — 0.98, Scale III — 0.93, Scale IV — 0.97, Scale V — 0.97, so the test scales have high discriminativity. Additionally some tests were carried out: the stability of the results of SEM analysis with a randomized division of the sample; gender differences; differences in groups according to the level of psychological competence. The questionnaire passed the necessary verification procedures, it can reliably serve theoretical and practical purposes.