The present study was conducted to investigate the effect of coding activities on children's mathematical reasoning skills. In the study, the pre-test - post-test control group quasi-experimental design was used. The participants of the study consisted of 29 children (17 in experiment group and 12 in control group) aged between 57 - 68 months attending a public kindergarten in Adana, Turkey. Coding Education Program prepared by the researchers was administered to the children in the experiment group while the children in the control group received the regular program. Evaluation Instrument for the Early Mathematical Reasoning Skills was administered to children both in the experimental and control group as pre-test and post-test. Data was collected by individual interviews conducted with the children. Results of the study showed that there is no significant difference between experimental and control group in the pre-test, whereas a significant difference in favor of the experimental group was observed in the post-test. Therefore, it was determined that the coding activities have a significant effect on mathematical reasoning skills of children.