Anti-phospholipase A2 receptor antibody (PLA2R-Ab) is useful for affirming the diagnosis of idiopathic membranous nephropathy (IMN). Time-resolved fluoroimmunoassay (TRFIA) is highly sensitive and quantitative for measuring serum PLA2R-Ab immunoglobulin (IgG). We measured PLA2R-Ab levels with TRFIA in sera from 172 patients with IMN (n = 69), secondary MN (n = 9), and those with other glomerulonephritis (n = 94) at the time of renal biopsy compared to healthy controls (n = 286). Serum anti-PLA2R-IgG levels in healthy volunteers ranged from 0.09-0.91 mg/L. We set the cutoff value of the anti-PLA2R-IgG titer at 0.91 mg/L, with a sensitivity of 84.06% for diagnosing IMN. Increasing the cut-off value to 2.025 mg/L altered the sensitivity for diagnosing IMN to 71.01%, but with 100% specificity. IMN patients had significantly higher serum anti-PLA2R-IgG levels compared to those with secondary MN. PLA2R-Ab titers negatively correlated with estimated glomerular filtration rate (eGFR). Patinets with high titers had significantly lower serum albumin and eGFR, higher proteinuria and serum creatinine levels, accompanied by a lower complete remission rate. High titers of PLA2R-Ab were associated with poor prognosis of patients with IMN. TRFIA-based quantification of anti-PLA2R-IgG can be a reliable approach for the diagnosis and prognostication of patients with IMN.