OBJECTIVE To explore the difference of bone formation potential between hypertrophic nonunion tissue and atrophic nonunion tissue, which may be beneficial to nonunion therapy. METHODS From October 2010 to March 2014, 40 nonunion tissue samples were collected in Department of Orthopedics, Second Xiangya Hospital. The samples were divided into a hypertrophic nonunion group (n=20) and an atrophic nonunion group (n=20) according to nonunion character; or a 20 to 35 years old group (n=18), a 36 to 50 years old group (n=18), a more than 50 years old group (n=4) according to different ages; or a 9-12 months group (n=21), 13-24 months group (n=14) and a more than 24 months group (n=5) according to different nonunion time. Semi-quantification was performed by SP immunohistochemical method and IPP6.0 was used to analyze the expression of bone morphogenetic protein-2 (BMP-2) through measuring the mean optical density. RESULTS The mean optical density of BMP-2 was 0.1540±0.0408 in hypertrophic nonunion tissue, 0.1372±0.0372 in atrophic nonunion tissue, there was no significant difference between the 2 groups (P>0.05). The mean optical density of BMP-2 was 0.1477±0.0379 in the 20 to 35 years old group, 0.1419±0.0399 in the 35 to 50 years old group, 0.1456±0.0595 in the more than 50 years old group, there was no significant difference among the three groups (P>0.05). The mean optical density of BMP-2 was 0.1449±0.0366 in the 9-12 months group, 0.1472±0.0400 in the 13-24 months group, 0.1445±0.0541 in the more than 24 months group, there was no significant difference among the 3 groups (P>0.05). CONCLUSION The present results suggest that the hypertrophic nonunion tissue share similar osteogenic potential with the atrophic nonunion tissue.