Leukemia threatens children's health, and leukemia cell proliferation and apoptosis participate in the regulation of leukemia. The current study aims to probe into the miR-125b-5p biological function in regulating leukemia cell proliferation and apoptosis by myeloid cell leukemia 1 (MCL1). Quantitative real-time polymerase chain reaction was conducted to quantify miR-125b-5p expression in leukemia cells. Cell transfection, cell-counting assay 8, Western blot, and flow cytometry assays were applied to assess the miR-125b-5p function in leukemia. A dual-luciferase reporter gene assay was applied to investigate the mechanism. miR-125b-5p was lessened in leukemia cells, and the increased miR-125b-5p repressed leukemia cell proliferation and boosted apoptosis. Further, miR-125b-5p could bound with the MCL1 3'-untranslated region and regulated its expression. Furthermore, the elevated expression of miR-125b-5p repressed leukemia cell proliferation and boosted apoptosis through downregulating MCL1. miR-125b-5p inhibited leukemia cell proliferation and boosted apoptosis through decreasing MCL1.