Abstract: The nicotine degrading behavior of a new strain capable of degrading nicotine, Agrobacterium tumefaciens B5, was studied and compared with that ofArthrobacter nicotinovorans. The results showed that:in the liquid medium of nicotine, the culture solution containingAgrobacterium tumefaciens B5 was grey, while that containingArthrobacter nicotinovorans was blue-black; in the solid medium of nicotine, the colony of Agrobacterium tumefaciens was grey at early growth stage, after that the color of colonies and plate turned gradually into brown-red with the prolongation of time; however, some blue substances were found at the early growth stage ofArthrobacter nicotinovorans, at the place where the colony was growing the color of the plate changed gradually from dark blue to blue-black, and eventually the entire plate turned into dark brown-yellow. It suggested that there possibly be significant differences of metabolic mechanism between the two bacteria. The results of nicotine degradation test in liquid medium indicated thatAgrobacterium tumefaciens B5 entered its logarithmic growth phase in about 10 hours, whileArthrobacter nicotinovorans in 6 hours, and the amount of thalli of B5 was higher than that ofArthrobacter nicotinovorans. However, the nicotine degradation efficiency of the two bacteria was similar after culture for 18 hours.