The effects of azadirachtin, a natural extract of the neem tree Azadirachta indica A. Juss, on larval growth and feeding activity of pine processionary moth (Thaumetopoea pityocampa (Schiff.)) was investigated in laboratory experiments conducted in 2007 - 2008. The organic insecticide NeemAzal-T/S (a commercial neem preparation) was applied as suspension in distilled water at concentration levels of 0.3, 0.5 and 1%. Comparing with the untreated leaves, the effect of the insecticide NeemAzal-T/S was tested on the 10th day after treatment. The results obtained in conducted experiments indicated that NeemAzal-T/S was effective against T. pityocampa larvae, significantly inhibiting larval growth and reducing feeding activity.