Great attention has been placed on the protective role of heme oxygenase-1 (HO-1) for several vascular diseases such as atherosclerosis. HO-1, by exerting anti-inflammatory, antiproliferative, anti-apoptotic and anti-oxidant effects on the vasculature, protects against atherosclerosis. The precise underlying mechanisms for HO-1-based protection are not yet completely understood, but appear to involve the protective effects of HO-1 by-products, carbon monoxide (CO), biliverdin/bilirubin and free iron. Among the HO-1 by-products, CO has been shown to mimic some protective actions of HO-1, specifically, in vascular system. There is evidence supporting that HO-1-derived CO also interacts with other gaseous molecules, such as nitric oxide (NO) and hydrogen sulfide (H2S) that may relate to either vascular protection or injury. CO, NO and H2S not only exert comparable biological actions but also compete with and are antagonists with each other for maintaining vascular homeostasis. This review will highlight the protective roles of HO-1/CO in vascular injury/disease, and emphasize the potential roles of CO in possible interplay among three gaseous molecules, which may be important to explore the overall protective roles of HO-1/CO system in the pathogenesis of human vascular disease.