We present an experimental investigation on the photophysical properties of meso-tetra(sulfonatophenyl) porphyrin (TPPS4) in its bi-protonated and deprotonated states in water solutions at pH 4.0 and 7.0, respectively. The Z-scan technique at 532 nm with single 70 ps pulses as well as with pulse trains, was used in association with other complementary techniques such as UV-Vis absorption spectroscopy and time resolved fluorescence. The saturation behavior and the time evolution of nonlinear optical absorption were analyzed with a five-energy-level diagram. Photophysical parameters such as ground and excited states absorption cross-sections, together with the fluorescence lifetime and intersystem crossing time were determined. © 2005 Elsevier B.V. All rights reserved.