Porphyrin derivatives are one of the major groups of compounds applied in photodynamic therapy. Their effect and interaction with different cell organelles and macromolecules is dependent on their chemical structure.We have examined the effect of the molecular structure of porphyrin derivatives on binding to liposomes without net charge and with negative charge. In this study a series of substituted tetraphenyl porphyrins (TPPs) has been used. Two of them, TP(4-OGluOH) 4 P and TP(4-OXylOH) 4 P, are symmetrically substituted derivatives having four carbohydrate -glucose or xylose -moieties linked to the macrocycle. The other two derivatives, TP(4-OGluOH) 3 P and TPF5(4-OGalOH) 3 P, were selected as asymmetrically substituted amphiphilic molecules with slightly different hydrophobic character due to the different ligand moieties. Association constants (K L ) of derivatives to liposomes and rate constants of liposome binding have been determined and also the gel-to-liquid-crystalline phase-transition parameters have been monitored in order to determine the type and strength of interaction. According to our measurements, the K L values follow the order TP(4-OGluOH) 3 P)TPF5(4-OGalOH) 3 P)TP(4-OXylOH) 4 P for both types of liposomes. TP(4-OGluOH) 4 P is able to bind only to vesicles holding negative charges on their surface. At 188C, the measured data are best fitted by two exponentials for three TPP derivatives. The binding of TP(4-OGluOH) 4 P follows single-exponential kinetics. At 378C, TP(4-OGluOH) 3 P binds to DMPC liposomes according to biexponential kinetics, but all the other binding processes follow monoexponential kinetics under similar conditions. The strongest effect on phase-transition parameters is caused by TP(4-OGluOH) 3 P. From the results it can be concluded, that the binding process of TPPs, especially that of the symmetrically substituted derivatives, is drastically influenced by the surface charges of the model membranes. According to present data, the negative surface charges of DMPC/DMPG liposomes can facilitate the association of the symmetrically substituted hydrophilic porphyrins to the liposomes. However, the asymmetrically substituted derivative TP(4-OGluOH) 3 P, which is the most lipophilic compound in the present investigation, still has the largest association constant to both neutral and negatively charged liposomes. In general, in both types of liposomes the order of the association constant follows the order of the lipophilicity of the porphyrin derivatives.