Abstract The Research was intended to increase children’s cognitive abilities through simple science experiments In Rainbow Playgroup at RT.11 village Pematang Gadung District Mersam. This study is a class action research. Studies are conducted in 2 cycles and each cycle were performed 2 meetings. The subject of this study is five or six years old kids in the group B and 14 children, consisting of 7 girls and 7 boys. The method used for data collections was observation and documentation. The results show that a child’s cognitive abilities in the rainbow playgroup at the beginning of 41% action in which 2 childrens begin was to developed cognitive abilities. In the 1 1st meeting cycle 59% of the children grew to 4, and then in the 1 2nd meeting 68% of the children grown to 7. And the results of the 2 1st meeting cycle were 78% of the number of children growing to 11, and then in the 2 2nd meeting cycle the result was 86% of the children growing to 12. The difference in improvement on pre-cycle to cycle 1 is 27% and cycle 1 to cycle 2 is 18%. The result of this study has already met the achievement indicators by 80%. The results of this study suggest thst simple scientific methods of experimentation can improved children’s children’s cognitive abilities.