PURPOSE: Autologous platelet rich plasma (PRP) has been known to enhance tendon healing and improve tensile strength after tendon injury. This study investigated the dosage of PRP to increase the tensile strength. METHODS: PRP was harvested from peripheral bloods of the rabbits. Direct injury model was adopted using 60 achilles tendons in 30 rabbits. The autologous PRP was infiltrated into the Achilles tendon repair site of four groups (control, 0.1, 0.2, 0.4 mL) with different dosages. Tendons were harvested at 2, 4 and 8 weeks and subjected to measuring mechanical tensile strength and dosage of collagen content. RESULTS: At 2, 4, and 8 weeks, PRP administration following experimental achilles tendon repair resulted in an overall higher average tensile strength and collagen content compared to these of the control. Also, the lengthen the time, tensile strength and collagen content was increased. CONCLUSION: Autologous PRP enhanced tendon healing in rabbits. Within the PRP dosage setted by the author, more dosage of the infiltrated PRP increases the strength of the tendon and the dosage of collagen content. Further studies will be essential to determine the optimal dosage of PRP in clinical practice.