Although a chlorophyll meter (SPAD) has become a simple, quick and portable diagnostic tool for monitoring leaf N status and improving the timing of N topdressing in rice, the problem is that inconsistent SPAD critical indices exist in N fertilizer recommendation for different leaf positions, and different measurement points of the same leaf. Up to now, there have been no reports in the li erature on standardization of the use of SPAD for N diagnosis in rice. Hence, the objectives of this study were (1) to improve the sampling method ofSPAD readings for rice N status diagnosis; and 2) to develop and optimize indicators based on SPAD indices to diagnose rice N status without the concerns of differences of rice genotypes and growth stages