Boron insufficiency in the agricultural soils is common and wide spread problem in many regions of the world. The effectiveness of crushed ore colemanite as B sources for rice crop under flooded calcareous soil were evaluated in a glass house study. We studied the effects of powder colemanite (PC) and granular colemanite (GC) in comparison with the refined sodium pentaborate fertilizer at the rates of 0, 1, 2, and 3 kg B ha^-1 on growth and yield parameters of rice crop as well as the true control (0 kg B ha^-1). Sodium pentaborate (SP) and (PC) application of 2 and 3 kg B ha^-1 significantly increased the plant height, number of tillers and panicles per plant, number of grains per panicle, weight of 1000 grains and B concentration in grain compared the 0 and 1 kg B ha^-1. Rice crop with SP and PC applied at 3 kg B ha^-1 produced significantly (18% over the control) higher grain yield than the 0 kg B ha^-1 treatment. Pots fertilized with SP and PC produced similar results as grain yield difference between them was not significant so these B fertilizers were very effective in supplying B to rice crop, but GC applied pots produced significantly low yield because of its bigger particle size, due to which B was not released from fertilizer. This study proved that colemanite with smaller particle size is an effective B source and it is cheaper than refined products so it should be applied for harvesting higher yields.