Two-dimensional numerical computations were performed to investigate non-absorbable gas diffusing behavior in the evaporator-absorber in an absorption chiller. In this paper, special attention was paid to the effect of initial condition of non-absorbable gas distribution. When non-absorbable gas is distributed uniformly in the evaporator-absorber, overall heat transfer coefficient does not markedly decrease until the mean concentration of non-absorbable gas becomes 5 vol%. On the other hand, when non-absorbable gas is injected at a point near the upper corner of the evaporator in the same way as in the experiments, overall heat transfer coefficient markedly decreases and agrees with the experimental results. This indicates that the initial condition of non-absorbable gas distribution seriously affects the heat transfer characteristics of the absorber. Under uniform initial conditions, non-absorbable gas is kept in the recirculation region formed between the evaporator and the absorber when the mean concentration of non-absorbable gas is small. Upon injection, however, non-absorbable gas penetrates deeply into the upper region of the absorber. This causes the recirculation region disappearance. Then, the heat transfer markedly decreases in the absorber.