Abstract: To study the toxic spectrum of Aspergillus niger, phytotoxicity, cytotoxicity as well as antimicrobial activity were taken as the test criteria. Culture filtrates of A. niger exhibited phytotoxicity against onion and tomato by reducing seed germination and root elongation. The culture filtrates were also tested for cytotoxicity using onion root tip bioassay. Cytological aberrations such as enucleate cells, transfer of chromatin material between adjacent cells and binucleate cells were found in treated onion root tips. Culture filtrates of the fungus grown on yeast extract sucrose broth for one month was extracted with different solvents. Concentrated solvent extracts were tested for antimicrobial activity using disc diffusion method. Butanol and ethyl acetate extracts of the fungal culture filtrates exhibited antimicrobial activity.