One of the most important properties of a stimulus is its location. The behavioral studies indicate that animals can perceive odor locations by comparing the time/concentration differences produced at the two nostrils. However, it is still controversial that the olfactory bulb, which is the first center in olfactory pathway, has the ability to encode the odor location information. To clarify the debate, we compared the responses of 84 mitral cells to three different odor stimulation modes in present study: odor to ipsilateral nose only, to contralateral nose only, and to both noses with the contralateral stimulation preceding the ipsilateral. We found that 29 cells showed excitatory responses to ipsilateral odor stimulation, and 18 of them showed no response to contralateral stimulation. However, the presence of the contralateral odor stimulation could significantly suppress the responses elicited by ipsilateral odor stimulation. In addition, 50 of the 84 cells showed no response when the ipsilateral or contralateral odor stimulation presented alone, but 11 of them showed excitatory responses when the odor stimulation presented to both noses with contralateral stimulation preceding the ipsilateral. The results indicate that the mitral cells of the olfactory bulb have the ability to encode the time difference of the odor arriving at the two nostrils, and that the contralateral odor stimulation can enhance the response through unknown neuronal pathways.