The electronic structures and properties of palladium-thiolate complexes, Pd-n(SCH3)(2n) with n = 6 and 8, have been investigated by carrying out density functional calculations. The complexes have characteristic tiara-like structures, that is, the palladium atoms form a hexagonal or octagonal ring and each adjacent pair of the palladium atoms is bridged by the sulfur atoms from both sides of the palladium ring. It has been found that Pd-S pi bonds play a crucial role in constructing and stabilizing such tiara-like structures. In fact, there exist the Pd-S pi bonding orbitals distributing throughout the tiara ring. The Pd-S pi bonding interaction also accounts for the reason Pd-n(SCH3)(2n) with n = 6 and 8 are much more stable than other complexes with different n.