|Many inflammatory mediators, including histamine, inflammatory proteases, arachidonic acid metabolites and cytokines are released by mast cell activation. However, little is known about the endogenous modulators for mast cell activation and their mechanism. Endogenous cannabinoids found in peripheral tissues, such as palmitoylethanolamide (PEA), have been proposed as having autacoid activity, which can down-regulate mast cell activation and local inflammation. Based on the chemical structure of agonists and antagonists, 30 compounds were synthesized and their modulating activity on human cannabinoid receptor 1 (CB1R) and 2 (CB2R) were tested using CB1R or CB2R transfected CHO cell line, respectively. Among the tested compounds, a few potential CB1R agonists were screened and further investigated on mast cell activation model. Using a cultured rat mast cell line, effect of selected compounds on Fcε RI-induced histamine and β-hexosaminidase release were measured. As a result, newly synthesized CB1R agonists down-regulated the release of histamine by IgE activation in mast cells, Furthermore, inhibitory effect on histamine release was also observed in mast cells activated by protease-activated receptor (PAR)-2 agonists. Taken together, CB1R agonists can down-regulate the mast cell activation, and might be a used for relieving inflammatory symptoms mediated by mast cell activation, such as atopic dermatitis, psoriasis, contact dermatitis or chronic urticarial.