Lipophilic anionic dichlorofluorescein ester was examined as a chromophore for the development of polymeric film based optical sensors for calcium. A calcium organophosphate salt and a neutral ionophore were employed as the active component for calcium sensing. The response pH. dynamic range, detection limit and selectivities are governed by the calcium carrier as well as the membrane plasticizer. The membrane that uses the anionic chromophore and the calcium organophosphate salt responds to calcium in the range of 1.0 × 10−6to 0.2 M at pH 7.4.