Fatty acid methyl esters (FAME) derived from catfish oil, were investigated for its potentiality as friendly substitute for commercial petroleum-based organic diluents to extract Co(II) over Li(I) from the simulated leaching solution using tris-2-ethylhexylamine (TEHA). The results showed that TEHAin-FAME diluent exhibited higher extraction efficiency of Co(II) and higher separation factor of Co(II) and Li(I) compared to the commercial diluents including kerosene, toluene, and hexane. About 97% of Co (II) from the simulated leaching solution containing Li(I) were obtained in counter-current extraction and stripping experiments by TEHA-in-FAME using dilute HCl solutions. The extraction capacity of the regenerated TEHA-in-FAME was almost unchanged after five recycling stages of extraction and stripping processes, indicating that FAME was an effective diluent for replacement of the commercial diluents.