Aim: to evaluate the bone healing in failed endodontically treated teeth after surgical enucleation of periapical lesions and packing of hydroxyapatite, and nanohydroxyapatite powder periapically. Subjects and methods: the study was established on sixteen patients having periapical radiolucency in single rooted teeth. The selected teeth were divided into two groups: Group A and Group B; of 8 teeth each. All the teeth were retreated in two visits. In the first visit the old filling was removed then irrigation with sodium hypochlorite was done. Di-antibiotic paste (ciprofloxacin and metronidazole) was used to fill the canals for 10 days. In the second visit the canals were obturated with Pro Taper gutta-percha points and root canal sealer followed by surgical intervention in the same day. Apicoectomy and periapical curettage were established. In both the groups, after preparation of root end cavity, it was filled with MTA followed by placement of regeneration material in the curetted periapical defect (hydroxyapatite (group A) and nanohydroxyapatite (group B)). In both groups, patients recall visits were scheduled at 1, 3, and 6 months time intervals for clinical and radiological evaluation. Results: after one month; there was a statistically significant difference between the median percentage changes in lesions size in the two groups. After three and six months; there was no statistically significant difference between the two groups. Conclusion: It was concluded that nanohydroxyapatite produced faster bone regeneration in the first three months than hydroxyapatite. However, hydroxyapatites produce bone regeneration after six months.