The structural, IR and magnetic properties of the mixed spinel Cu1+xMnxFe2-2xO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) system have been investigated by means of X-ray diffraction, Infrared spectroscopy, magnetization and a.c. susceptibility measurements. X-ray results confirm single-phase spinel structure for all the concentrations. The structure of CuFe2O4 is tetragonal and changes to cubic for x = 0.1 to 0.4. For x = 0.5 and 0.6 the structure become tetragonal. The lattice parameter and X-ray density are deduced and their variation with Mn4+ concentration is studied. The cation distribution derived from the X-ray diffractometry data was found to agree very well with the cation distribution obtained from magnetization measurements. X-ray intensity calculations indicate that Mn4+ occupy only octahedral [B] sites and Cu2+ and Fe3+ ions occupy both octahedral [B] and tetrahedral (A) sites. The infrared spectra obtained at room temperature in the range 200-800 cm(-1) showed two absorption bands. The force constants have been obtained from IR data. The variation of the saturation magnetization per formula unit as a function of Mn4+ content x has been satisfactorily explained on the basis of Neel's collinear spin ordering model for all values of x. The Curie temperature T-C determined from a.c. susceptibility data decreases with increase of Mn4+ concentration x, suggesting decrease in ferrimagnetic behaviour.