ABSTRACT Water lettuce (Pistia stratiotes) is one of the problematic aquatic weeds because it can cause many problems for humans and environment. In addition, the declining quality and quantity of water is also due to the invasion of water lettuce weeds covering the surface of waters, which can lead to the increasing transpiration and destruction of plankton making the balance of the ecosystem disrupted. This study was conducted in an attempt to control water lettuce (Pistia stratiotes) by utilizing the biological control agent Spodoptera pectinicornis with mass production and its releasing applications in South Kalimantan’s waters. The study was started by collecting S. pectinicornis from several places/ fields. The moths were then placed in trays of water and put in a gauze cage of 75 cm x 75 cm x 75 cm in order to keep the air circulation. They were nourished in a laboratory to produce groups of eggs. The groups of eggs were then transferred to rearing ponds. When a fair number of agents were obtained, the treatment of liquid fertilizer AB Mix was carried out. The results showed that the treatment with fertilization to water lettuce weeds as the feed for the biological control agent S. pectinicornis did not make any difference when compared to the treatment without fertilization either in S. pectinicornis’ feeding ability, weight of larvae and pupae or in fitness of imago. However, its destructive ability is so high that it has a big potential as a biological control agent of water lettuce. Keywords: Mass production, Spodoptera pectinicornis, Pistia stratiotes