In addition to initiating signaling cascades leading to mast cell mediator release, aggregation of the high affinity IgE receptor (FcεRI) leads to rapid internalization of the cross-linked receptor. However, little is known about the trafficking of the internalized FcεRI. Here we demonstrate that in RBL-2H3 cells, aggregated FcεRI appears in the early endosomal antigen 1 (EEA1+) domains of the early endosomes within 15 min after ligation. Minimal co-localization of FcεRI with Rab5 was observed by 30 min, followed by its appearance in the Rab7+ late endosomes and lysosomes at later time points. During endosomal sorting, FcεRIα and γ subunits remain associated. In Syk-deficient RBL-2H3 cells, the rate of transport to lysosomes is markedly increased. Taken together, our data demonstrate time-dependent sorting of aggregated FcεRI within the endosomal-lysosomal network, and that Syk may play an essential role in regulating the trafficking and retention of FcεRI in endosomes.