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To assess whether drinking tea can effectively prevent smoking-induced atherosclerosis, a clinical trial ex vivo study was performed. The volunteers were randomly allocated to two groups (n = 55 per group) that received either Pu-erh tea powder or a cellulose placebo (0.5 g/capsule, T.I.D.) for two months. The circulating monocytes were isolated from the tested individuals after 0, 1, and 2 months of tea-capsule administration. We found that monocytes displaying high α9-nicotinic-acetylcholine-receptor (α9-nAchR) expression that were isolated from heavy smokers before consuming tea capsules tended to form foam cells in response to nicotine (1 µL for 24 h, *P < 0.001). In contrast, long-term tea consumption significantly downregulated the monocytic α9-nAchR expression (0 months vs. 1 and 2 months; #P = 0.013 and ##P = 0.004, respectively) which causes circulating monocytes to resist nicotine-induced foam cell formation even in heavy-smokers (*P < 0.001). This study suggests that tea-drinking effectively attenuates the initial step (foam-cell formation) of smoking-induced atherosclerosis in circulating monocytes.