Abstract: The biology of cashew stem and root borers Plocaederus ferrugenius L. and P.obesus Gahan (Coleoptera: Cerambycidae) was studied on cashew bark under laboratory conditions. In case of Plocaederus ferrugenius L the mean grub period was recorded 163.10 ± 20.55 and 168.37± 30.32 days, mean pupal period was 144.33 ± 29.57 and 145.16 ± 29.10 days for males and females, respectively. The total development period ranged between 261-363 days (male) and between 242-356 days (female). In case of Plocaederus obesus Gahan., mean grub period was 152.75 ± 31.35 and 158.49 ± 33.26 days, mean pupal period was 142.90 ± 22.57 and 152.34 ± 38.46 days for males and females, respectively. The total developmental period ranged from 226 to 379 days and 247 to 347 days for males and females respectively. The duration of grub stage was more than 40 per cent of the total life duration of Plocaederus spp. The details of adult morphometrics of P.ferrugenius L. indicated that in case of males, the mean body length was 38.8 mm; mean body width being 8.76 mm and mean body weight being 0.89 g; the females had mean body length of 33.5mm; mean body width of 10.29 mm and mean body weight of 1.39g . The morphometric details of adults of P.obesus males indicated a mean body length of 38.6 mm; mean body width of 8.63 mm and mean body weight of 1.4 g, while females had mean body length of 36.6 mm; mean body width of 9.31 mm and mean body weight 1.76 g. In both the species, the length of pro, meso and meta thoracic legs did not differ significantly, wing to elytra length was in the ratio of 1: 0.9.