The chlorophyll meter (SPAD) and leaf colour chart (LCC) are simple, portable diagnostic tools that can measure the crop N status in situ in rice fields to determine the timing of N top dressingAn experiment was carried out in Rice Research Institute in Mazandaran, in 2019. A test material has been evaluated in a Randomized Complete Block Design with three replications. Tarom variety were grown under eight treatments at plant density of 25*25 cm. Eight treatments included a zero-N control, o splits, chlorophyll meter 35, 37, 40, LCC 4 and 5. Result showed that Both LCC and SPAD can be used to improve N management for rice. The optimal SPAD threshold for determining the timing of N-application was 35. LCC treatments indicated that N-management based on LCC shade 4 helped avoid over application of N. Critical value of LCC 4 was more beneficial in enhancing the growth and agronomic, physiologic and internal efficiency. It is suggested that when N-management technology such as real time N-management (SPAD and LCC) were used, would avoid to over application of N fertilizer by rice farmers. The objective of this study is to determine critical threshold SPAD and LCC value of Tarom variety of rice(Oyiza Sativa L).