In vivo studies were conducted to assess the allelopathic effects of eucalyptus leaf, bark and root extracts at different concentration gradients (1.0 to 10.0%) on the germination and seedling growth of cucumber germination and seedling growth were severely affected by leaf extract than those of bark and root. Germination percentage and seedling growth were severely hampered as concentration gradient increased from 1.0 to 10.0 per cent. The interaction effect of leaf extract at 10 per cent concentration resulted in the lowest germination percentage and poor seedling growth.