Electrocatalytic oxidation of formaldehyde on a glassy carbon modified with electropolymerised films derived from tetrakis(4-hydroxy-3-methoxyphenyl)porphinato nickel(II) (THMPPNi(II)) was studied in 0.1 M NaOH on stationary and rotating electrodes by cyclic voltammetry and rotating disc amperometry, respectively. The data from rotating disc experiments were analysed according to Albery-Hillman theory. The findings showed that the poly-THMPPNi(II) behaves as an efficient electrocacalyst for the oxidation of formaldehyde with the cross-exchange reaction occurring throughout the layer at a low concentration of formaldehyde and for a thin modifier, i.e. the mediating process corresponds to the Lk kinetic case, with a change over to the LEk regime at higher substrate concentration or for thicker films.