Two new pentavalent molybdenum chloromonophosphates, KMoOPO4Cl and RbMoOPO4Cl, have been synthesized. They crystallize in theP4/nmmspace group witha=b=6.4340(5) andc=7.2715(9) Å for the potassium compound anda=b=6.4551(8) andc=7.4612(8) Å for the rubidium compound. Their original structure consists of [MoPO5Cl]∞layers parallel to (001), whose cohesion is ensured by K+or Rb+ions. The chloride ions and the alkali metal cations form a puckered rock salt layer.