To investigate the root canal numbers of maxillary second primary molars.

216 maxillary second primary molars from 204 children aged 3-8 years old were selected. All the teeth need to do the root canal therapy. After opening the pulp chamber, the root canal were examined and determined with small size K file and 17% ethylene diaminetetraacetic acid (EDTA). Hand instruments were used for root canal preparation and then zinc-oxide iodoform paste was used for filling.

216 maxillary second primary molars, 122 teeth had three root canals (56.5%), and 94 teeth had four root canals (43.5%). The incidence of second mesiobuccal canal (MB2) was 41.2%. There was no correlation between the incidence of the MB2 canal and gender and tooth position.

The root canals of maxillary second primary molars had more variations, and there was a high incidence of the second mesiobuccal canal.