The present study examined children's understanding about psychological, physical and biological phenomena. Children aged 3, 4, 5, 7, 9, and 11(16 at each age) participated. They were given s series of questions, which measured children's understanding of psychological knowledge(intension, belief, false-belief, trait), physical knoweldge(solidity, falling1(garvity), falling2(garvity+weight+air resistance buoyancy), and biological knowledge(energe exhaustion, growth, heredity, infection) and examined how they have changed with increasing age. The results showed that the psychological domain was indepentent from 3 year of age and childres's psychological knowledge existed as a form of naive theory in terms of their use as a causal devise in explaining the cause of psychological phenomena. However, in the physical domain, the knowledge system has changed after 9 years of age respectively and older children employed causal mechanism more frequently and relied less on the perceptual properties. In the biological domain, it changed dramatically from 3 to 5 years of age. In the energy exhaustion task, a few children used a psychological causal devise in explaining the cause of biological phenomena. The findings of the present study suggests that children's knowledge about psychological, psysocal and biological phenomena develop specifically each domain with increasing age.