We introduce a multiuser (MU) scheduling method for amplify-and-forward (AF) relay systems, which opportunistically selects both the transmission mode, i.e., either one-or two-hop transmission, and the desired user. A closed-form expression for the average achievable rates is derived under two transmissions with MU scheduling, and its asymptotic solution is also analyzed in the limit of large number N of mobile stations (MSs). Based on the analysis, we perform our two-step scheduling algorithm: the transmission mode selection followed by the user selection that needs partial feedback for instantaneous signal-to-noise ratios (SNRs) to the base station (BS). We also analyze the average SNR condition where the MU diversity gain is fully exploited. In addition, it is examined how to further reduce a quantity of feedback under certain conditions. The proposed scheduling algorithm shows the comparable achievable rates to those of optimal one using full feedback information, while its required feedback information is reduced below half of the optimal one.