The composition and stability of the complex formed between diphenyltin dichloride, Ph2 SnCl2, and Na-3-alizarin sulphonate, alizarin red-S, have been studied spectrophoto- metrically in dilute ethanolic Solutions. The effect of rise in the temperature, from 22-60° C, on the stability of the complex is recorded. No direct change in colour was observed when dilute ethanolic solution of stannous chloride was added to alizarin red-S, but it was found that the complex requires 2-3 days to be formed. Some physical properties of the red solid complex obtained from the reaction of Ph2 SnCl2 and alizarin red-S are reported.