The LB films forming properties of two hydroxyl-substituted porphyrins with double hexadecyl chains have been characterized. UV-Vis spectra show that the two porphyrins possess various aggregation behaviors in LB films. The porphyrin with symmetrically attached chains tend to form J-aggregate and the other asymmetric porphyrin can form hydrogen-bonded aggregate in LB films. The orientation of porphyrin rings was examined by polarized UV-Vis spectra. The results indicate that the situation of side-chain attached on porphyrin ring has no influence on porphyrin ring orientation, but has great influence on mean molecular areas or the distanses between porphyrin rings, and so as to affect the aggregation behaviors of porphyrin in LB films.