Substituent effect on the thirdpe order optical nonlinear properties and their excited state relaxation processes in porphyrins have been studied. In the samereplacement on phenyl of tetraphenylporphyin, we discovered that the X(3) value of H2TPP increased with donating electron group and decreased with withdrawing electron group relative to that of free base H2TPP. As the same substituent at different bearing on phenyl of tatraphenylporphyring, the X(3) value of H2TPP with donating electron group at ortho place is less than that at para place. Moreover, we found that the relaxation time of H2TPP with donating electron group is about 7 times faster than that with withdrawing electron group.