Melanoma is an aggressive skin carcinoma with poor prognosis, and is prevalent worldwide. It was demonstrated that microRNA (miR)‑21 and mitogen‑activated protein kinase kinase 3 (MKK3) both participated in the occurrence and development of various tumors; however, their detailed roles in the progression of melanoma remain unclear. Reverse transcription‑quantitative PCR (RT‑qPCR) and western blot analyses were conducted to examine the expression levels of miR‑21 and MKK3 in clinical specimens of patients with melanoma and melanoma cell lines. A dual‑luciferase reporter assay was performed to verify the target interaction between miR‑21 and MKK3. The mRNA and protein expressions of MKK3 were measured using RT‑qPCR and western blot analysis, respectively, following transfection with miR‑21 mimics and inhibitor. Subsequently, Cell Counting Kit‑8 and colony formation assays, and flow cytometry were conducted to assess the effects of miR‑21 and MKK3 on the cell growth of melanoma. Cell migration and invasion experiments were performed to evaluate the effects of miR‑21 and MKK3 on the cell metastasis of melanoma. It was revealed that MKK3 was upregulated, and miR‑21 was downregulated in patients with melanoma and melanoma cell lines. MKK3 was demonstrated to be a direct target of miR‑21. Furthermore, it was demonstrated that upregulated miR‑21 expression and downregulated MKK3 expression suppressed cell proliferation and colony formation, promoted apoptosis, delayed the cell cycle, and inhibited cell migration and invasion. The present findings suggested that miR‑21 could inhibit the cell growth and metastasis of melanoma by negatively regulating MKK3.