Nanotechnology plays a unique and novel role to develop new methods for adjuvant preparation, which play an important role in the efficacy of vaccines. In this study we have studied the effects of Calcium phosphate nanoparticles (CaP) <150 nm particle size measuring with Electron microscope, on the magnitude and type of immunity elicited in response to inactivated FMD trivalent vaccine. A comprehensive sero-immunological study was conduced to reveal the adjuvant's effect of Calcium phosphate nanoparticles on the immune response to oil adjuvanted trivalent Foot and Mouth Disease (FMD) in vaccinated calves. This study was conducted in three calve groups; group (A) vaccinated subcutaneously with trivalent oil FMD vaccine, group (B) vaccinated subcutaneously with trivalent FMD vaccine adjuvanted with Calcium Phosphate nonaoparticles (10 mg/dose).While group (C) vaccinated subcutaneously with trivalent FMD vaccine adjuvanted with both oil and CaP nanoparticles. The humeral and cellular immunoresponses were monitored in different tested groups. Results indicated that the incorporation of Calcium phosphate nanoparticles into inactivated FMD vaccine induces an increase of the specific protective immune response. Higher and longer period of immune responses were found in calves vaccinated with both oil and Calcium phosphate nanoparticles adjuvanted vaccine up to 40 week, while those vaccinated with Calcium Phosphate nanoparticles and with oil vaccine showed protected immunity up to 36 and 32 weeks respectively.