Correlation between mental development and emotional state in 5-7 years old children when constricting a square was studied. The children were divided into two groups: with low level of functional development (group A) and with high one (group B). For group A emotional processes (assessed by speech changes) were more marked out and labile than for group B. When negative emotion was formed by insoluble task in the beginning of the experiment motivation level on the last stage of it was dependent on individual ability to solve such a task. Group A children's actions were characterized by spontaneity, action appraisal appeared at its final stage and was accompanied by homogeneous, mostly negative, emotion. Group B children marked out the objectives of their activity, evaluated its success and their emotions were contradictory. Motivation for task solving decreased more in group A than in group B.