CCD images of quasars having redshifts between 0.3 and 0.65 are analyzed to study the association of galaxies with quasars. Average luminosity functions (LF) of the excess galaxies associated with the radio-loud quasars are determined. It is found that for the sub-sample with z>0.55, there is a significant brightening of the characteristic magnitude M*, if qo is assumed to be 0. Comparing computed quasar-galaxy spatial-covariance amplitudes, we can conclude, at the 0.025 significance level, that the spatial-covariance amplitudes of the sub-sample with z>0.55 are greater than those of the lower redshift quasars. This indicates that there has been a strong evolution of preferred sites for bright radio-loud quasars, implying some number-density evolution of quasars has taken place, and that some rich clusters at z∼0.6, in comparison with the local rich clusters, have significantly different physical conditions.