Entomopathogenic nematodes are soil-dwelling biocontrol agents. EPNs need an insect host to complete their life cycle, and they kill their host during its development. The major disadvantage of EPNs is the high cost of commercial products. Thus, there are many studies focused on reducing production costs by optimization of mass production. In a previous project, Heterorhabditis bacteriophora Poinar, 1976 (Rhabditida: Heterorhabditidae) HBH hybrid strain was developed from local isolates. This hybrid strain was patented due to superior bioecological characteristics. This study aimed to optimize in vitro solid mass production of hybrid strain. All laboratory trials were performed between 2017 and 2018, in Nematology Laboratory of Bursa Uludag University, Faculty of Agriculture, Department of Plant Protection. For optimization, additional supplementary ingredients (soy lecithin and egg yolk), temperature (24, 28 and 32 degrees C) and medium pH (5, 7 and 9) were selected as production parameters. Optimization was evaluated based on hermaphrodite egg numbers, total infective juveniles (IJs), IJ body length and IJ virulence. Based on results, best production combination was found as agar containing soy lecithin, 28 degrees C and pH 7. Also, agar media with pH 9 markedly reduced production yield. Consequently, optimum values for some important in vitro solid production parameters of HBH hybrid strain were determined.