Hepatocellular carcinoma (HCC) is the most common liver cancer and has a poor prognosis. miR-302a is an important regulator of tumor occurrence and deterioration, while MAP3K2 and PBX3 genes are involved in cancer cell proliferation and apoptosis. In this study, the expression of miR-302a and MAP3K2/PBX3 were evaluated by qPCR in liver cancer cell lines. Next, the target relationship between miR-302a and MAP3K2/PBX3 was verified using luciferase assays. Meanwhile, the expression correlation between miR-302a and target genes was analyzed in cancer tissue and para-cancerous tissue. In addition, an increased miR-302a level in HepG2 cells and SMMC-7721 cells were achieved through transfection with miR-302a mimics, and the effects on HepG2 cell and SMMC-7721 cell proliferation, apoptosis and MAPK pathways were determined using MTT, flow cytometry, qPCR and western blot assays. The results showed that liver cancer cell lines exhibited low miR-302a expression and MAP3K2 and PBX3 were confirmed to be the target genes of miR-302a. Meanwhile, the HE results showed that cells became enlarged with loose cytoplasm and formed balloon-like lesions in HCC specimens and we found a significant negative correlation between miR-302a and MAP3K2/PBX3 expression. In addition, treatment with miR-302a mimics inhibited HepG2 cells and SMMC-7721 cells proliferation and increased the apoptosis rate. Further research revealed that the MAPK key factors p-p38, p-ERK1/2 and p-JNK were significantly reduced in miR-302a transfected cells and MAP3K2/PBX3 silenced cells. Besides, MAP3K2 and PBX3 overexpression in miR-302a mimics-treated cells exerted the opposite effects. In conclusion, miR-302a inhibited proliferation and promoted apoptosis in human hepatoma cells by targeting MAP3K2 and PBX3.