A pot culture experiment was conducted on rice to study the critical limit of boron in soils of old alluvial zone of West Bengal. The hot water soluble (HWS) boron in these soils was found to be positively and significantly correlated with organic carbon, clay content and per cent dry matter yield of rice, boron concentration in plant tissues and B uptake by shoots. A negative relationship was also observed between WHS boron and silt and sand content. The critical concentration of soil available boron and plant tissues boron was worked out to 0.38 and 15.0 mg kg^-1, respectively. Soil containing available B below the critical limit responded appreciably to B fertilization. A negative response to boron application was also observed at its higher level. The average dry matter yield increases with increasing level of boron application up to 1.5 mg kg^-1 in boron deficient soils. The response to boron application in rice on boron deficient soils was found to be 52.5%.