Long noncoding RNA MCM3AP-AS1 plays critical roles in cancers, but its role in atherosclerosis is yet to be elucidated. The expression of MCM3AP-AS1 in atherosclerosis and control plasma samples were measured by RT-qPCR. IntaRNA was used to predict potential base pairings between MCM3AP-AS1 and miR-448, and the results were confirmed by a dual luciferase activity assay. Cell proliferation assay was performed to explore the role of overexpression of MCM3AP-AS1, miR-448, and myocyte enhancer factor 2 (MEF2)-C in the proliferation of human aortic smooth muscle cells (HAOSMCs). MCM3AP-AS1 was downregulated in atherosclerosis and directly interacted with miR-448, which is a critical player in the proliferation of HAOSMCs, indicating its involvement in atherosclerosis. However, MCM3AP-AS1 and miR-448 showed no role in regulating the expression of each other. In contrast, overexpression of MCM3AP-AS1 increased the expression levels of MEF2-C, which can be targeted by miR-448. Moreover, MCM3AP-AS1 was found to inhibit the effects of miR-448 overexpression on both HAOSMC proliferation and MEF2-C expression. MCM3AP-AS1 is downregulated in atherosclerosis and sponges miR-448 to suppress the proliferation of HAOSMCs.