The radial forging strain-induced melt activation (RFSIMA) is adopted to process the as-extruded 6063 aluminum alloy. In this research, the influence of radial forging on the microstructure of as-extruded 6063 aluminum alloy has been investigated. The semi-solid microstructural evolution generated by the directly semi-solid isothermal treatment, and initially radial forging predeformation and then semi-solid isothermal treatment have been analyzed. The results indicated that the compaction degree of RF-deformed 6063 aluminum alloy microstructure gradually increases as the area reduction increases. However, this increasing pattern is not obviously when the area reduction increases from 70% to 85%. In addition, the more ideal semi-solid microstructure can be obtained through RFSIMA as compared with the directly semi-solid isothermal treatment.