The peritoneal tumor is not named after the originating of cancer cells but instead contains all tumors appearing in the region of the peritoneal cavity. There are over 250,000 new cases of malignant diseases originating from organs in the peritoneal cavity annually in the USA, and most of these cases spread by intraperitoneal seeding. Cytoreductive surgery for removal and debulking of metastases in the peritoneal cavity is the primary treatment option. Complete surgical removal of the cancerous tissues, however, is difficult to achieve because positive margins are often left behind, and it is difficult to detect the small metastases in the peritoneal cavity. Methyl aminolevulinate (MAL), a protoporphyrin X (PplX) prodrug, has been clinically used for photodynamic therapy of local malignancies such as Basal Cell Carcinoma and Actinic Keratosis. Its application for cancers in the peritoneal cavity, however, has been limited by its non-specific biodistribution and adverse effects. Since nanoparticles can play an essential role as drug deliver platforms as a result of their loading capacity, sustained drug release profile, and potential targeting ability, I proposed a liposomal delivery system, Folic-modified liposome (FL). The goal of this study is to take advantage of this observation by developing a FL system of MAL for photodynamic diagnosis and therapy of cancers in the peritoneal cavity in a more specific and efficient manner. Based on the results presented, FL has the potential to improve cytoreductive surgery in the following manner: a) A hydrophilic core can encapsulate high amounts of MAL and protect it from metabolic degradation; b) FL systems loaded with MAL can enlarge the gap between PpIX accumulation in tumor cells and normal tissues. c) FL system loaded with MAL can provide photodynamic diagnosis and photodynamic therapy as complementary functions. / Pharmaceutical Sciences