Nematode yield is a decisive factor for successful large-scale commercial production of entomopathogenic nematode. Various carbon sources were tested in in-vitro liquid culture to improve the yield of the entomopathogenic nematode Heterorhabditis bacteriophora. Canola oil was the optimal carbon source for nematode culture compared to carbohydrates when applied as a sole carbon source. However, when some of carbohydrates were applied together with canola oil, significant increases in nematode yield were observed. When 25 mg glucose ml(-1) was supplemented to 25 mg oil-based liquid culture medium ml(-1), the highest nematode yield, 3.62x10(5) infective juveniles, was achieved at 12 days, but nematode growth was suppressed at higher than 75 mg glucose ml(-1). A fed-batch culture process was introduced in nematode liquid culture consisting of two growth phases: bacteria and nematode. In the oil fed-batch culture, in which only glucose was initially added and oil was fed to the culture after the bacterial growth phase concurrent with nematode inoculation, nematode yield increased up to 4.25x10(5) infective juveniles ml(-1), while the batch culture resulted in 3.60x10(5) infective juveniles ml(-1). These results indicate that glucose is a superior carbon source for the bacteria, whereas canola oil is optimal for the nematode. The application of fed-batch culture provides significant enhancement of nematode yield in in-vitro liquid culture.