Substituent effects on aurophilic interactions have been explored by single-crystal X-ray diffraction methods for a series of Au(I) complexes of monodentate phosphines, R' 3 P Au X (X=Cl, Sph, and Spy). When a CF 3 substituent is introduced at a meta position of the phenyl ring in (C 6 H 5 ) 3 P, aurophilicity has been accrued in ClAuP(m-CF 3 C 6 H 4 ) 3 . However, aurophilicity has been weakened by introducing two CF 3 groups at both meta positions. When a CF 3 substituent is substituted for a H atom in the para position or when a CH 3 substituent is introduced in the meta and/or para positions, such an effect has not been observed for R' 3 PAuCl and R' 3 PAuSph. Most dimers constructed by aurophilicity appear to be reinforced by π-π interactions between the phenyl ring of the Sph ligand or the pyridine ring of the Spy ligand and one of the phenyl rings in the R' 3 P ligand. A novel ladder-like supra molecular architecture is created in the crystal of {3,5-(F 3 C) 2 C 6 H 3 } 3 PAuSph, and a tetramer is formed in the crystal of (C 6 H 5 ) 3 PAuSpy by aurophilic and π-π interactions. Substituent effects on important bond lengths have been discussed.