Objective: To estimate the biological characteristics of HA gradient coating in vivo.Method:We inserted coated and uncoated implants in bilateral femur of loading area in dogs.Result:Histological findings demonstrated that HA coated implants bind the host bone tightly and the amount and velocity of the new bone formation are more than the uncoated implants.The mean interface shear strength between HA gradient coated implants were greater than those of uncoated implants (p<0.01).Conclusion:The results of this study confirms that HA gradient coatings can has its practical value in orthopeadics fields.