The BCL-2 protein family plays central roles in the mitochondrial pathway of cell apoptosis. The BCL-2-Associated X protein (BAX), along with other proapoptotic proteins, induces cell death in response to a variety of stress stimuli. Upon receipt of killing signals, cytosolic BAX is activated and translocates to mitochondria where it causes mitochondrial outer membrane permeabilization (MOMP) and initials a series of cellular events that eventually lead to cell destruction. Despite recent progress toward understanding the structure, function, and activation mechanism of BAX, detailed information about how cytosolic BAX can be inhibited is still limited. Here we describe a method of selecting synthetic antibody fragments (Fabs) against BAX using phage display. Synthetic antibodies discovered from the selection have been used as structural probes to gain novel mechanistic details on BAX inhibition. This synthetic antibody selection method could be potentially applied to other BCL-2 proteins.