Scanning laser manipulation and microspectroscopic techniques were applied to analyze a molecular association of malachite green (MG) in single water droplets dispersed in dioctyl phthalate. Droplet size effects on MG dimer formation were observed in micrometer dimension; dimer formation was facilitated in the smaller water droplets. Concentration effects of MG and an added electrolyte on dimer formation were also studied in detail, and the results were discussed in terms of Langmuir-type adsorption of the MG dimer at the water droplet/oil interface.