Abstract: A study of sulfur-gold sensitization on AgBr(I) emulsion used in the astrophoto-graphy was carried out, in which the effects of conditions of chemical sensitization such as the time interval between the addition of sulfur sensitizer and gold sensitizer and the ratio of sulfur to gold in weight on the photographic speed and low intensity reciprocity failure of the emulsion were experimentally investigated. The results showed that a significant improvement of the photographic performance of the emulsion could be obtained by choosing proper conditions of chemical sensitizatiou. In the present case the optimum time interval between the additions of the two sensitizers was 60 minutes and the optimum ratio of sulfur sensitizer to gold in weight was 3.5.