In the course of their work, psychologists must make judgments and complex decisions, skills that are part of clinical reasoning. Recent models approach the analysis of such process using the dual-process theories framework. This study provides an assessment of the two systems, System 1 and System 2, in forty-five clinical psychologists with different levels of experience (novices, intermediates and experts) with the purpose of exploring their level of activation and evolution throughout such stages of expertise. According to the results, clinical psychologists mainly activate System 2, M = 70.91, SD = 6.71, than System 1, M = 60.49, SD = 3.78; $ {F}_{\left(1,\kern0.5em 41\right)}=7.99;p<.01;{\upeta}^2=.163, $ when performing their clinical duties. However, no significant changes have been observed regarding the preferential use of thinking Systems 1 or 2 throughout the experience, both systems are used in a similar way in the different levels of expertise analyzed, with an increase of System 2 at the intermediate level of expertise. The results are analyzed in terms of intermediate effect and discussed focusing on the unremitting need for System 2 in psychologist work given the idiosyncratic characteristics of each case requiring treatment in the area of psychology and on the relationship of the two systems in clinical reasoning.