The biological control potential of entomopathogenic nematodes (EPN) can be enhanced by improved culture efficiency. Optimization of the media is a key factor for improving in vitro mass production of entomopathogenic nematodes. This study reports the effect of medium concentration. The medium is a combination of carbohydrates, lipids, proteins, sats, and growth factors, on the growth of Heterorhabditis bacteriophora and its symbiotic bacterium Photorhabdus liminescens. The overall optimal medium concentration for nematode recovery, hermaphrodite size, bacterial mass, infective juveniles (IJs) yield, and doubling time was 84 g/l. At this concentration rate, the doubling time of IJs production and the biomass of symbiotic bacteria was 1.6 days and 12.8 g/l, respectively. The maximum yield of $2.4{ imes}{10^5}IJs/ml$ was attained within a one-generation cycle (eight days). The yield coefficient was $2.8{ imes}{10^6}$ IJs/g medium, and the maximum productivity was $3.1{ imes}{10^7}$ IJs per day. Medium concentration affected two independent factors, recovery and hermaphrodite size, which in turn influenced the final yield.