TASK-3 is a member of the acid-sensitive subfamily of two-poredomain K⁺ channels. We recently demonstrated that the adapter protein 14-3-3 interacts with the distal cytoplasmic C-terminus of TASK-3 and regulates channel trafficking to the surface membrane. Here we describe another mechanism that contributes to the regulation of the surface expression of TASK-3. A di-acidic sequence motif (EDE) in the proximal cytoplasmic C-terminus of TASK-3 was identified as a putative endoplasmic reticulum export signal. Wild-type (wt) TASK-3 channels and mutants in which the EDE motif was replaced by ADA were expressed in Xenopus oocytes or COS-7 cells. Whole-cell measurements in Xenopus oocytes showed that the ADA mutant produced much less current than wt TASK-3 channels. Surface expression analysis of HA-tagged TASK-3 channel proteins revealed strong intracellular retention of TASK-3 ADA mutants. Live cell imaging of EGFP-tagged channels in COS-7 cells showed labelling of the surface membrane 24 h after transfection of wt TASK-3. In contrast, the ADA mutant was hardly detectable at the surface membrane, but showed predominant endoplasmic reticulum localization at that time point. We conclude that the di-acidic endoplasmic reticulum export motif EDE is necessary for efficient surface expression of TASK-3.