A two-dimensional numerical study on a vapor flow with non-absorbable gas in the absorber-evaporator of an absorption chiller has been performed to investigate where the non-absorbable gas exists in the device. In a rectangular numerical domain, 80 cylinders for an evaporator and 96 cylinders for an absorber were mounted. The mean concentration of non-absorbable gas was changed from 0 to 10vol% in the computations. From the present results, non-absorbable gas is found mainly to concentrate in the upper region between evaporator and absorber, because the adverse flow is formed in the region. This adverse flow is weakened as the mean concentration of non-absorbable gas increases. Then, the high concentration region of the non-absorbable gas moves toward the absorber. This causes that the gas penetrates deeply into the absorber, and that the decreasing rate increases as the mean concentration increases.