This work reports photo-demetallation studies of thin-layer, electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) loaded with low levels of: (i) an anionic Mn porphyrin monomer (5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato manganese(III) chloride (MnTPPS)), and (ii) an anionic Mn porphyrin polymer (poly(5-(4-vinylphenyl)-10,15,20-tris(4-sulfonatophenyl)) porphyrinato manganese(III) chloride (MnPVTPPS)). UV-vis and other measurements confirm that, like previously-studied cationic Mn(III) porphyrins embedded within vapour-phase polymerized PEDOT in low loadings, de-metallation under light illumination also occurs in these systems. However, it occurs to a significantly lesser degree. It can be concluded that demetallation appears to be an inherent feature of PEDOT coatings containing low levels of Mn porphyrins when they are illuminated with light. The demetallation process does not depend on the mode of polymerisation or the nature of the Mn porphyrin dopant. These findings have potentially important implications in water-splitting photocatalysis by Mn porphyrin-doped conducting polymers.