The effects of Neem Azal T/S and Neemix preparations obtained from Azadirachta indica A. Juss. were investigated on development larvae of Leptinotarsa decemlineata Say. A. indica preparations were tested to be alternative to chemical insecticide to control L. decemlineata. Bioassays to determine the effect of varying concentrations of extracts were used in three different methods. Third instar larvae of about 30-35 mg weight were used for leaf dipping, larvae dipping and topical application. For all experiments 2.2 cm in diameter leaf disks obtained from potatoes grown in the glasshouse were used. For three bioassays four different concentrations were used, for Neem Azal T/S 15, 25, 50, 100 ppm and Neemix 10, 15, 30, 60 ppm. All of experiments were repeated six times. The results were determined at larvae stage that duration of larvae and pupae periods have been prolonged for all the methods, high mortality at larvae and pupae stages have been obtained, malformed individuals came out, number of individuals from pupae were decreased and the number of eggs laid by the healthy females of the treated pupae decreased.