Abstract: Strains of Botryodiplodia theobromae collected from mango in Hainan of China were used to characterize their resistance to carbendazim and fitness. The resistance of 90 B. theobromae strains to carbendazim was detected using distinguishing dosage method. Fitness of resistant strains was compared with sensitive strains from the aspects of mycelial growth rate, pathogenicity, osmotic pressure and electroosmosis rate. The results showed that the resistance frequency of strains to carbendazim was 65.56% and the major resistant type is of high resistance (8 medium resistant strains and 51 high resistant strains). The B. theobromae strains have high hazard to mango. And there were 65 highly virulent strains accounted for 72.22% of the whole population. The mycelial growth rates of the resistant strains and the sensitive strains were significantly different at the 0.01 level between. However, there were not significant differences in the pathogenicity. The relative conductivity of sensitive strains mycelia was higher than that of the resistant strains. It indicated that the cell membrane permeability of the sensitive strains was higher, which led to the leakage of a large number of cell electrolyte.This study showed that strain of B. theobromae has high resistance to carbendazim, the fitness of resistance strains is better than that of sensitive strains.