X-ray analysis of Na2KSb a photoemissive material discovered by Sommer has led to the determination of its crystal structure. The unit cell is described by the space group Fm3m-01l5 with four antimony atoms at (0,0,0; O,t,!; t,O,t; t,t,O) + 0,0,0; four potassium atoms at ( ) + t,t,! and eight sodium atoms at ( ) + t,t,t and t,t,t. The crystal structure of Na2KSb has a great resemblance to that of CS3Sb and differs strongly from that of Na3Sb and K3Sb which both crystallize in the Na3As type.