The outcome of systemic lupus erythematosus (SLE) is largely influenced by the existence of lupus nephritis (LN), and its histologic classification guides the treatment and prognosis of SLE. International Society of Nephrology-Renal Pathology Society (ISN-RPS) announced a revised classification of LN in 2004. The present study investigated the differential outcome of World Health Organization (WHO) class III LN when reclassified according to ISN-RPS classification. Forty-three patients with biopsy-proven WHO class III LN at a single tertiary hospital were included in the study. Baseline characteristics at the time of renal biopsy and clinical data during follow-up were obtained from medical records. Renal response to treatment at one-year follow-up was analyzed in three ways; complete response (CR), partial response (PR), and no response (NR). Of 43 patients with previous WHO class III LN, 12 cases were reclassified into ISN-RPS class IV (9 cases of class IV-S and 3 cases of IV-G). Baseline characteristics at the time of renal biopsy were not different between the reclassified class IV and remaining class III LN group except activity index on renal histology, which was significantly elevated in the reclassified class IV group (4.90 vs. 6.75; P = 0.02). Significantly higher number of patients with remaining class III LN achieved CR to treatment than those with reclassified class IV LN at one-year follow-up since initial biopsy (CR: PR: NR; 16:7:7 vs. 3:1:8; P = 0.032). Our study suggests that the ISN-RPS classification is more advantageous in predicting renal outcome and guiding treatment when evaluating previously classified WHO class III LN.