Introduction. Without appropriate treatment, nerve injuries may result in permanent loss of function. Platelet-rich plasma (PRP) injection is found to help in nerve regeneration. PRP is a concentrated platelet derived from autologous blood with the potential to release various growth factors (GF) to promote nerve regeneration. This study aims to know the best time for PRP injection to promote nerve regeneration. Methods. This is an experimental in vivo research using male New Zealand white rabbits in the randomized control group posttest only design. Samples were divided into 5 groups (1 control group and 4 treatment groups). The control group without PRP injection and treated groups injected immediately after nerve injury, 3 days, 7 days, and 14 days afterward. Nerve regeneration was evaluated by the histology specimen sacrificed on day 21. Inflammation cells and endoneurium vacuoles were counted as mean percentage of five nerve fragments in each injured nerve sample specimen. Result. Inflammation cells and vacuole cells increased significantly when PRP was administered 3 days after injury (group 2) (respectively, 14 ± 6.7 and 56.6 ± 11.6) compared to all treatment groups (p<0.005) (control group, respectively, 6 ± 2.6 and 15.7 ± 9.5). On the other hand, significantly lower endoneurium vacuoles and inflammation cells were found on "the day 14"sample group (respectively, 5 ± 1.3 and 5.2 ± 1.6) compared to all other groups (p<0.005). Conclusion. This study found that the best time for injecting PRP for nerve regeneration is 14 days after injury.