The critical area of spatial integration was examined in dichromatic vision (protanope and deuteranope) by means of chromatic thresholds at equiluminance. The results showed that the critical area became smaller as the chromatic saturation of the background field was increased. Here, the chromatic saturation was defined by the colorimetric purity of the background field, multiplied by the saturation coefficient (Cs) of each dominant wavelength. For the 470-nm field condition, the trend of dichromatic data was similar to that of the previous data with normal subjects. For the 590-nm condition, however, the decrease of integration area was less than that of the normal. This discrepancy can be attributed to the difference of saturation coefficients between normals and dichromats.