The study aimed to improve children's cognitive development through number card activities at 3-4 years old in TK (Kindergarten) Pembina Ulujami. The number of children in this study was 18, consisting of 8 boys and ten gifs. This research utilized the Classroom Action Research (CAR) method. The study was conducted in two cycles, with each cycle consisting of 3 meetings, and the methods used were observation, interviews, and documentation as data collection techniques. The data analysis technique employed in this research was qualitative data analysis. The results of the study consisted of two cycles of classroom action research. At the initial stage of cognitive development through number cards, the children's progress was low, with 11 children (61%) underdeveloped, three children (17%) beginning to develop, and four children (22%) developing as expected. After conducting the Classroom Action Research (CAR) in Cycle I, there was an improvement observed, with one child (6%) underdeveloped, ten children (55%) began to develop, three children (17%) developing as expected, and four children (22%) well developed. However, this result was not yet optinal, hence the continuation of Cycle II. The results obtained in Cycle II indicated the success of the research in achieving the predetermined development target. There were no underdeveloped children, one child (6%) began to develop, nine children (50%) developed as expected, and eight children (44%) developed very well. The researcher's conclusion indicated that nine children (50%) were classified as Developed as Expected (DAE), and elght children (44%) were classified as Well Developed (WD). The total success rate was 94%, indicating the success of this research.