Abstract: The HPLC analysis of four porphyrin photosensitizers including three China-made products (YHPD-Jiguan #3, HPS and LFO19) and photofrin Ⅱ indicated that they contained different amounts of hematoporphyrin, 3(8)-(1-hydroxyethyl)-8(3)-vinyldeuteroporphyrin, protoporphyrin as well as dihematoporphyrin ethers (DHE). Photofrin Ⅱ contained the highest content of DHE. The content of hematoporphyrin was highest in HPS, but relatively low in YHPD and LF019. The content of dihematoporphyrin ethers in LF019 was very close to that in YHPD. LFO19 was found to contain the highest percentage of protoporphyrin. The behaviors of the four porphyrin photosensitizers on the Bio-gel p-10 column were different, indicating differences in their aggregation states. The TLC of the four photosensitizers themselves or their methyl esters suggested the complexity of their composition. The UV, IR and ¹HNMR spectra were measured. The results of the survey of different effects on the aggregation state showed that the concentration, pH, organic solvents, irradiation and temperature may cause changes of the aggregetion slate of the products in solution. YHPD and LFO19 could form relatively more stable aggregates than HPS. But the aggregate of photofrin Ⅱ was much more stable.