Potentiometric pKa and polarographic behaviour of 1, 3-indandione-monoxime and four of its substituted derivatives were investigated in buffer solution of pH ~ 2-12. The results showed that the compounds are in the azo-form, where its reduction wave precedes that of the oxime. A mechanism for the electrodic processes was proposed. Half-wave potentials showed fair cor- relation with Hammett’s er constants while pKa is practically independent.