Biodesulfurization is regarded as a promising alternative technology for desulfurization from diesel oil due to its mild operating conditions and its ability to remove sulfur from alky dibenzothiophenes (C-x-DBTs). The diesel oil contains complex mixtures of C-x-DBTs in which individual microbial biodesulfurization may be altered. In this work, interactions among three typical C-x-DBTs such as dibenzothiophenes (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were investigated using Mycobacterium sp. ZD-19 in an airlift reactor. The experimental results indicated that the desulfurization rates would decrease in the multiple C-x-DBTs system compared to the single C-x-DBT system. The extent of inhibition depended upon the substrate numbers, concentrations, and affinities of the co-existing substrates. For example, compared to individual desulfurization rate (100 %), DBT desulfurization rate decreased to 75.2 % (DBT + 4,6-DMDBT), 64.8 % (DBT + 4-MDBT), and 54.7 % (DBT + 4,6-DMDBT + 4-MDBT), respectively. This phenomenon was caused by an apparent competitive inhibition of substrates, which was well predicted by a Michaelis-Menten competitive inhibition model.