Abstract: An investigation was made for yield and biomass in rice interactions of nitrogen and phosphorous fertilizer application under irrigated conditions. The objective of the experiment was to quantify nitrogen, phosphorous and water use and their combined effects on biomass and yield of rice. A routine management practice was performed in rice fields to maintain a water depth that would suppress weed growth during the growing season. Field experiments were conducted over the period of 1st week of July to 1st week of November, 2003 in Shuangqiao farm at northern part of Zhejiang province in southeast coastal area of China and Jia-9312 rice variety was used. Biomass and yield of rice were determined in comparison with the nitrogen and phosphorous fertilizer treatment and water use. The rice biomass increased rapidly during N2 (180 kg N) treatments and then decreased. Also, positive effect on rice biomass for phosphorous application was observed. Both water and fertilizer (N and P) had a positive effect on yield, which increased from 5.8 to 7.8 t ha-1. Grain yield increased on average by 2 t ha-1 by applying 180 and 40 kg P ha-1 fertilizer with sufficient water supply. Maximum dry weight of total paddy plant was observed in N4P2 treatment. From this experiment it was concluded that the yield of rice increased 50-60% in response to the application of N and P interaction with water.