Abstract CD300a is an inhibitory receptor for mast cells and eosinophils in allergic inflammation (AI); however, the spatiotemporal expression of CD300a and its potential roles in the resolution of AI are still to be determined. In this study, employing a mouse model of allergic peritonitis, we demonstrate that CD300a expression on peritoneal cells is regulated from inflammation to resolution. Allergic peritonitis–induced CD300a−/− mice had a rapid increase in their inflammatory cell infiltrates and tryptase content in the peritoneal cavity compared with wild type, and their resolution process was significantly delayed. CD300a−/− mice expressed lower levels of ALX/FPR2 receptor on peritoneal cells and had higher levels of LXA4 in the peritoneal lavage. CD300a activation on mouse bone marrow–derived mast cells regulated ALX/FPR2 expression levels following IgE-mediated activation. Together, these findings indicate a role for CD300a in AI and its resolution, in part via the specialized proresolving mediator LXA4 and ALX/FPR2 receptor pathway activation.