Biodiesel is conventionally produced by alkali-based transesterification, which is limited by the presence of water and the free fatty acid content of oil feedstock. This study investigated the potential of metformin (1,1-dimethylbiguanide) as an alternative organic base catalyst for the transesterification of coconut oil with methanol. Two parameters were considered in this work, the catalyst loading and the amount of water in the feedstock. When no water is present in the feedstock, metformin showed a significant FAME yield of 55 ± 8% at 1.0% w/w catalyst/oil. Increasing the amount of metformin to 2.0% w/w significantly increased FAME yield to 71 ± 4%. In the presence of water (5.0%, w/w water/oil) however, the catalytic performance of metformin was practically lost, with FAME yields of only 5.5 ± 0.3% (1.0% w/w catalyst/oil) and 2.6 ± 0.4% (2.0% w/w catalyst/ oil). Overall, metformin showed the ability as a catalyst for the transesterification of coconut oil with methanol. However, its efficiency is limited only to conditions where the water level in the feedstock is minimal.