The use of chemical pesticides in the context of pest control in mustard (Brassica juncea L.)plants is very dangerous. The used of biological agents of Steinernema spp. in the control of important pests is biological pesticide to overcome the problem of vegetable pest problems is e new hope foe us all so that farmers no longer us chemical pesticides that can interfere with human health. The utilization of biological agent in the form of election of entomopatogen nematode exploration on wetland from district of Barito Kuala, South Kalimantan. Test of biological agent formulation that is capable not only inhibits the development of plant pests (biopesticides). Experiment used a completely randomized design with each treatment ranging from control (without Steinernema spp.), 20, 40, 60, 80 and 100 tail population per unit, experiment with 3 repetitions, with 40 tail caterpillar as feed in mass propagation). The result of the study is that the population of entomopathogenic nematodes develops well in all treatment of Steinernema spp. DMRT test results showed that there were differences between treatments tested, only T1 and T2 treatment were not different in effect, because different initial population. Population with an initial population number of entomopathogen nematodes 80 and 100 tail tended to differ significantly and were stable in the number of late population development observations. In general that the use of caterpillar T. molitor is suitable in mass breeding entomopathogen nematodes.