Photodynamic therapy (PDT) is clinically approved, minimally invasive therapeutic procedure characterized by cytotoxic activity against tumor cells and various pathogens. It is based on dynamic interactions between the photosensitizer (PS), light of a certain wavelength and molecular oxygen, which lead to the destruction of the target tissue. One of the key components of PDT is PS selection and design. Most of the PSs used in PDT are based on porphyrin structure due to their favorable photophysical properties. Amphiphilic porphyrins are important for clinical application since they enable passive tumor targeting, which has previously been proven to be more effective than active targeting. Their hydrophobic parts enable them to enter and accumulate in cells, while hydrophilic parts make them soluble in water, which is important to prevent their aggregation and facilitate administration. It has been proven that hydrophobicity of porphyrins increases with the length of the alkyl chains and as a consequence their accumulation in tumor cells also increases. It is thought that the presence of an epoxy unit on the long alkyl chain of porphyrin could increase its antitumor activity since it has previously been shown that epoxidized fatty acids and some of their metabolites possess antitumor activity. In this thesis, the optimization of synthesis of N-methylated tripyridylporphyrin conjugated with long alkyl chain (18C) containing a polar group was performed. The effectivness of newly synthesized porphyrin and previously synthesized N-methylated tripyridylporphyrin conjugated with a long alkyl chain (18C) for use in PDT on human epithelial breast adenocarcinoma cells (MDA-MB-231) was compared. The newly synthesized compound, although effective, is less effective than previously synthesized one. However, it does not possess dark toxicity on MDA-MB-231 cells, unlike the compound that does not posess a polar group on the alkyl chain.