A new isoreticular metal-organic framework Zn(4)O(FMA)(3).xG (1; FMA = fumarate; G = guest molecules) of a primitive cubic net was synthesized and structurally characterized. With intersecting pores of about 6.8 x 6.8 A, the activated 1a exhibits high gas adsorption with respect to H(2), CH(4), and CO(2).