The interactions of tetracyanoethylene (TCNE) with 4-substituted meso-tetraphenylporphyrins (H2T(4-X)PP) results adducts of composition 2:1 of TCNE to H2T(4-X)PP, [(TCNE)(2)H2T(4-X)PP)]. Formation constants, K, as well as other thermodynamic parameters, Delta H degrees, Delta S degrees, and Delta G degrees of adducts were determined by UV-vis titration method. Adducts have positive values of Delta S degrees and Delta H degrees. These interactions are favorable with considerable negative values of Delta G degrees. Adducts stabilities are in the order: H2T(4-OCH3)PP > H2T(4-CH3)PP > H2TPP > H2T(4-Cl)PP.