TBC1D9B (TBC1 Domain Family Member 9B, also known as GRAMD9B or KIAA0676) is located on human chromosome 5q35.3. TBC1D9B belongs to the TBC family of GAP for the RAB proteins. It contains two GRAM domains, one TBC domain, and one EF-HAND domain. TBC1D9B may act as a GTPase-activating protein for Rab family protein(s). TBC1D9B has calcium ion binding and GTPase activator activity. An important paralog of this gene is TBC1D9.