The crystal and molecular structure of [Cu 2 (CH 3 COO) 4 (Hbet) 2 ] (Hbet=betaine: N,N,N-trimethylglycine: trimethylammonioacetate) was determined by a single-crystal X-ray diffraction method. The complex has a water-wheel-like structure which appears in [Cu 2 (CH 3 COO) 4 (H 2 O) 2 ]; the carboxylato oxygen atom of Hbet is coordinated to a copper atom instead of to a water molecule. The magnetic moment of this complex is 1.46 BM, which suggests the existence of an interaction between copper atoms.