This paper is about the effect of sport participation on self-esteem, anxiety, psychological immune system, and achievement motivation among early adolescents. Sample: 47 athletes (handballers) and 46 non-athletes boys took part in this research (age: 11-13 years). Methods: Coopersmith Self-esteem Inventory (Coopersmith, 1984), Spielberger State-Trait Anxiety Inventory for Children (STAI, Spielberg, 1973), Achievement Motivation Scale (Tóth, 2005) and Psychological Immune System Inventory Junior (PIK-J, Oláh, 2005). Results: sport increases self-esteem and coping, decreases anxiety and achievement motivation. Furthermore, these factors are not independent so positive changes in one field cause positive changes in others as well.