This study determined the genotoxic effects of Ganoderma lucidium and Pleurotus ostreatus on Allium cepa root tips. Small bulbs of Allium cepa were grown in different concentrations of aqueous extracts of milled Ganoderma lucidium (0.3g/ml, 0.6g/ml, 0.8g/ml, 1.0g/ml) and Pleurotus ostreatus (0.25g/ml, 0.75g/ml, 1.25g/ml, 1.75g/ml). Five root tips from each bulb were harvested after 48 hours and processed for cytological studies using aceto-orcein squash techniques. The average length of root bundles was determined after 96 hours. Treatment with P. ostreatus extracts seemed to inhibit root growth in a concentration-dependent manner while that of G. lucidium did not inhibit root growth. Extract mitotic index (M.I.) was calculated for each extract concentration. The M.I. for Ganoderma lucidium extracts were: 7.1 (0.3g/ml), 5.7 (0.6g/ml), 6.2 (0.8g/ml), and 4.5 (0.1g/ml), whereas M.I. for Pleurotus ostreatus extracts were 6.7 (0.25g/ml), 6.3 (0.75g/ml), 6.0 (1.25g/ml) and 5.4 (1.75g/ml). In the root cells, extracts from both test samples revealed chromosome stickiness, vagrant chromosomes, spindle multipolarity, c-mitosis, and bridged fragments.