Oil-continuous microemulsion phase behavior formed by formamide (polar phase), n-octane (oil phase), tri(ethyleneglycol)monododecyl ether (AEO3) was investigated. Using the methyl orange (MO) and methylene blue (MB) as absorption probes, the microstructure of nonaqueous microemulsions was probed with UV-vis spectroscopy measurements as the absorption maximum is changed with the polarities of the pure solvents, micelles and reverse-micelles systems. The results indicated that an n-octane continuous structure with formamide nano-droplets formed in formamide/ AEO3 /n-octane system.