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We have studied the effect of thermal-relaxation on the short-range order in Zr80Co20 metallic glass by means of differential scanning calorimetry, X-ray diffraction, electrical resistivity and the superconducting transition temperature, Tc. Experimental values for the crystallisation temperature and activation energy of the crystallisation processes were derived by studying these processes at different heating rates. The Tc of the Zr80Co20 metallic glass thermally relaxed with a heating rate of 60 K/min to slightly below its first crystallisation exotherm is higher than in unrelaxed Zr80Co20 metallic glass, whereas in all the other thermally relaxed samples Tc decreases with decreasing heating rates and increasing temperature of relaxation. The homogeneity of the thermally relaxed Zr80Co20 metallic glass is discussed by using the superconducting transition width as a criterion. The superconducting transitions of thermally relaxed Zr80Co20 metallic glass samples are characterised by a sharp fall in electrical resistance. This suggests that the samples are homogenous on a spatial scale of less than the zero-temperature coherence length ξ0. The position of the first maximum broad diffraction halo in XRD is shifted to smaller values of 2α with increasing temperature of relaxation and decreasing heating rates indicating an increase in the nearest-neighbour distance. [Copyright &y& Elsevier]