The characteristics, performance and application of membrane electrode based on ion associate of diclofenac with base dye Safranine T are described. The electrode response to diclofenac has the sensitivity of 47 ± 1.0 mV decade-1 over the range of 5 × 10-5 to 5 × 10-2 mol/L at pH 6-12, and the detection limit of 3.2 × 10-5 mol/L. The electrode is easy assembled at a relatively low cost has fast response time (2-4 s) and can be used for a period up to 3.5 months without any considerable divergence in potential. The proposed sensor displayed good selectivity for diclofenac in the presence of different substances. It was used to determine diclofenac in pharmaceuticals by means of the standard addition method.