Hydroxysafflor yellow A (HSYA) is the main active ingredient of edible plant safflower. HSYA has demonstrated anti-inflammatory effects. The inflammatory response is the key mechanism responsible for asthma, and the pro-inflammatory platelet-activating factor (PAF) is known to play a role in the pathology of bronchial asthma. In this study, we stimulated human bronchial smooth muscle cells (HBSMCs) with PAF and examined the effects of HSYA on the resulting asthma-related process. PAF stimulation induced HBSMC activation, induced proliferation, increased expression of the pro-inflammatory cytokines interleukin (IL)-6, IL-1 beta, and tumor necrosis factor-alpha, and activated asthma-related signaling pathways. All these effects were significantly inhibited by treatment with HSYA (9, 27, 81 mu mol L-1). The effects of HSYA were prevented by the addition of a PAF receptor (PAFR) antagonist or by PAFR gene silencing with small interfering RNA. These results suggest that HSYA may inhibit PAF-induced activation of HBSMCs by targeting the PAFR. Overall, these findings provide evidence that HSYA can be applied as a potential therapeutic agent in the treatment of bronchial asthma.