The self-assembly of mixed monolayers (mixed SAMs) on gold substrates using mixed dialkyl disulfide adsorbates is reported. This work was undertaken to probe the factors that control monolayer formation in these systems and to provide a basis for comparison with mixed SAMs formed from mixtures of alkyl mercaptan adsorbates. Gold-supported thin films were formed from three symmetrical and two mixed disulfides : di-n-octadecyl disulfide (4), di-n-butyl disulfide (5), di-tert-butyl disulfide (6), n-butyl n-octadecyl disulfide (7), and tert-butyl n-octadecyl disulfide (8). As benchmarks with which to compare thin films formed from mixed dialkyl disulfides, two series of mixed SAMs formed from combinations of n-octadecyl mercaptan (1) and either n-butyl mercaptan (2) or tert-butyl mercaptan (3) were prepared. Surfaces were characterized by contact angle goniometry with water and hexadecane probe liquids, optical ellipsometry, X-ray photoelectron spectroscopy (XPS), and negative ion time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was found that the adsorption efficiencies of 1-3 varied in the order 1 > 2 >> 3. A 3-4-fold excess of 2 to 1, and a 40-100-fold excess of 3 to 1 were required to produce mixed SAMs with equal concentrations of butyl- and n-octadecyl adsorbates, indicating the preferential adsorption of longer-chain species in these systems. In contrast, no preference for adsorption of longer-chain species was observed with the mixed disulfide adsorbates 7 and 8, which produced mixed SAMs with apparently equal surface concentrations of n- or tert-butyl- and n-octadecyl groups. Evidence from TOF-SIMS suggests that both butyl- and octadecyl mercaptide groups are present in thin films formed from 7 and 8, and at concentrations similar to those present in 1:1 mixed SAMs formed from mixtures of alkyl mercaptans 1 + 2 or 1 + 3. SAMs formed from dialkyl disulfides appear to be formed under kinetic control and not to undergo appreciable exchange with dialkyl disulfides in the deposition solution.