Atherosclerosis (AS) is a frequently occurring cause of cardiovascular disease and involves a complicated pathophysiological process. Studies suggest that long non-coding RNAs (lncRNAs) are involved in AS genesis and progression, but mechanisms underlying these connections are unclear. Therefore, this work focused on exploring the role of lncRNA CASC7 in AS. In this study, RNA-seq sequencing results identified 1040 lncRNAs differentially expressed between AS patients and healthy controls. Of these lncRNAs, 458 were up-regulated and 582 were downregulated. CASC7 was found to be down-regulated in serum samples from AS patients and in HUVEC and VSMC exposed to ox-LDL. Overexpression of CASC7 inhibited proliferation and enhanced apoptosis of VSMC, and it markedly reduced IL-1β, IL-6 and TNF-α levels in HUVEC. Increased expression of a CASC7 target, miR-21, abolished the effects of CASC7 on HUVEC and VSMC. Notably, miR-21 targets PI3K in VSMC and TLR4 in HUVEC. The inhibitory effect of CASC7 was decreased by stimulation of PI3K, suggesting that the CASC7/miR-21 axis functions through PI3K/Akt signaling in VSMC. Similarly, the inhibitory effect of CASC7 on the inflammatory response in HUVEC was abolished through activating the TLR4/NF-κB signaling pathway. CASC7 inhibited proliferation and enhanced the apoptosis of VSMC through modulating the miR-21/PI3K-AKT axis, and upregulating CASC7 suppressed the inflammatory response of HUVEC by sponging miR-21 to inhibit the TLR4/NF-κB signal pathway.