Prostaglandin D_2 is a major lipid mediator released from activated mast cells of which metabolite 9α,11β-prostaglandin F2 are used as a biomarker of mast cell activation in various type of asthma. Prostagladin D_2 acts on DP_1 (DP, PTGDR), CRTH2 (DP_2) and TP receptors resulting in bronchoconstriction and airway eosinophilia and increase of Th2 cytokines. Several single nucleotide polymorphisms of DP and CRTH2 has been reported to be associated with asthma susceptibility in some population. Thus, prostaglandin D_2 may play an important role for the pathogenesis of asthma. Therefore, prostaglandin D_2 could be a potential new therapeutic target for asthma. Indeed, several CRTH2 antagonists are currently under investigation for the treatment for asthma. Here, this review will summarize the biosynthesis of prostaglandin D_2 and its receptors and focus on the role of prostaglandin D_2 in the pathogenesis of asthma including genetic association studies.