Tetrakis(4-sulfonatophenyl)porphine tetraanion (H2TPPS4-) forms a noncovalently linked dimer at low concentration in aqueous solutions at pH 9.0 in the presence of potassium ion and crown ether. The fluorescence decay of the dimer is double exponential with Lifetimes (and amplitudes) as follows : 8.82 ns (0.91) and 2.14 ns (0.09). The fluorescence anisotropy decay for the dimer (tau(r) = 2.36 ns in 30% sucrose solution) is slower by a factor of 2 than that of the monomer. The cation-crown ether dimer complex may consist of only one crown ether. The major component (8.82 ns) of the fluorescence decay is attributed to the H-dimer and the minor component (2.14 ns) to the J-dimer. At pH 3.5 the protonated form of H2TPPS4- (the dianion H4TPPS2-) forms J-aggregates upon increasing the ionic strength. The average aggregation number for the J-aggregate is estimated to be 22 from the anisotropy decay time of 10 ns. The fluorescence decay of the J-aggregate is multiexponential with the 50 ps component as the major one.