Ruminal Solubility of Certain Calcium Sources such as calcium carbonate, calcite, dolomite, lime stone powder and dicalcium phosphate (DCP) powder was investigated. Solubility of these calcium sources was low at pH 7 and ranged from 1.74 ± 1.36 in Dolomite to 2.94 ± 0.95 percent in Dicalcium phosphate (DCP). Reducing the pH of the ruminal buffer at 6 increased their solubility and the pattern was almost similar to that recorded at pH 7. Further reduction of pH of ruminal buffer to 2.5, increased their solubility significantly (up to 72.63%), however, Ca solubility of calcium carbonate and dolomite was lower than the other calcium supplements. It was concluded that calcite and lime stone powders may be good source of Ca under the conditions when ruminal pH is towards lower side.