An investigation of the nonlinear absorption of a wide range of structurally diverse porphyrin monomers, bisporphyrins and trisporphyrins, using open Z-scan technique with 6 ns pulsed laser operating at 532 nm was carried out. Using the theory of reverse saturable absorption, the intensity dependent nonlinear absorption coefficient βeff was deduced from the experiments. Monomers which Soret band maximum was situated closer to the experimental wavelength had higher βeff. The βeff of dimers and trimers were in the same range as for monomers. The highest βeff = 5.3 10-8 cmW-1 was found for a zinc complex of 5,15-A2B2 type porphyrins with 3-methoxyphenyl and trimethylsilyl-ethynyl groups in the meso positions. ; PUBLISHED ; Science Foundation Ireland (Research Professorship SFI 04/RP1/B482, SFI 06/RFP/CHO044 and SFI 08/CE/I1432)