Sclerotium rolfsii is one of the devastating soil-borne phytopathogens which causes severe loss at the time of seedling development. It also causes leaf spots in several crops and wild plants. Petri plates, containing potato dextrose agar medium, were inoculated with S. rolfsii. Two-third area of three, 50% area of three and 100% area of other three plates were sealed with cellophane tape. The other three plates were not sealed. All the plates were incubated at 27±2°C. Two sets of such plates were prepared. One set was incubated in light whereas the other set in the dark. There was no significant difference in mycelial growth and number of sclerotia among them but significant difference was observed when compared to the control, i.e. the plates which were not sealed. Sclerotium and basidiospore formation were directly influenced by air as completely sealed plates failed to produce sclerotia and basidiospores. Basidiospores were produced abundantly in the light and in the dark conditions in unsealed plates only on Cyperus rotundus rhizome meal agar medium.