We proposed an improved method based on the ethane efflux method of C ameron and Yang for measuring the resistance to gas diffusion in plant tissues. The effect of temperature and fruit size on the resistance and the conversion from the resistance to ethane diffusion to that to gaseous O₂ and CO₂ diffusion were also investigated using citrus Iyo fruit (Citrus iyo hort. Ex Tanaka). The results were in good agreement with those of the original method, and were obtained in a shorter amount of the time. The resistance to ethane diffusion depended on both the temperature and fruit size; specifically, the higher the temperature, the lower the resistance and the larger the fruit size, the higher the resistance. Finally, we presented equations to predict the resistance to O₂ and CO₂ diffusion using values measured with the ethane efflux method.