The selectivity in the synergistic extraction of cadmium (II) and zinc (II) with a mixture of thio-thenoyltrifluoroacetone (STTA) and a pyridine base was surveyed. The degree of synergistic effect of a pyridine base in the extraction of cadmium (II) was more remarkable than in the case of zinc (II). As a result, preferential extraction of cadmium (II) could. be performed. In order to attain the complete separation of cadmium (II) from zinc (II), we employed 2, 2'-dipyridyl (dipy), which might act as an additive in cadmium (II) extraction due to possible formation of an adduct Cd (STTA)₂(dipy) and at the same time, this reagent is expected to work as a masking agent for zinc (II). The procedure for the separation is as follows: Twenty ml of an aqueous solution. containing 0.1 M sodium chloride (pH=3.6) is equilibrated with an equal volume of 1×10^-3 M STTA and 0.1 M 2, 2'-dipyridyl in 1, 2-dichloroethane by shaking the mixture for 10 min. Only cadmium (II) is selectively extracted into the organic phase.