The solvent viscosity dependence of the photophysical and photochemical properties of tetra(tert-butylphenoxy)phthalocyaninato zinc(II) (ZnTBPPc) is presented. The fluorescence quantum yields (ΦF) and Stern-Volmer′ s constant (KSV) for ZnTBPPc fluorescence quenching by benzoquinone in all the solutions followed a semi-empirical law that depends only on the solvent viscosity. ΦF values vary between 0.08 in tetrahydrofuran (THF) and 0.14 in dimethylsulphoxide (DMSO). Triplet quantum yields (ΦT) and lifetimes (τT) also exhibit clear solvent viscosity dependence with the values being higher in the most viscous solvents. The interaction of the ZnTBPPc triplet state with oxygen was found to be diffusioncontrolled, but higher rate constants were observed in low-viscosity solvents like THF and toluene. Absolute values of singlet oxygen quantum yields (ΦΔ) were determined, and the values are comparable in all the solvents, which is attributed to the proximity of the ZnTBPPc triplet energies in different solvents.