Strain Pseudomonas sp. I-24 (I-24) cannot utilize iopromide (IOP) as the sole carbon and energy source, so different carbon sources (starch, malt sugar, glucose and glycerol) were used as the additional carbon sources to study their effects on I-24 growth and IOP degradation in flask tests. The results showed that the IOP degradation process by I-24 matched the first-order kinetics. Among these four co-substrates, starch was found to be the most efficient to enhance IOP degradation. The corresponding degradation efficiency was as high as 92.7% and the highest enzymatic activity of 0.182 mU appeared in the third day. The optimum starch concentration was 1 g x L(-1). Since glucose and malt sugar better promoted I-24 growth and electron transport system activity (ETSA), indicating that the IOP degradation process would probably be restrained by excess growth, which decreased the degradation efficiency of IOP. In addition, no direct correlation between ETSA and co-metabolism process was found. The detected enzymatic activity of I-24 in control sample indicated that the key enzymes could be still induced in low-concentration of co-substrates.