Beauveria bassiana (Balsamo) Vuillemin, an entomopathogenic ecologically friendly fungus was tried in the laboratory and at the screen house to test for the potency of the fungi against varying stages of the fall armyworm larvae. Five IITA maize varieties were used to determine the efficacy of ten isolates of B. bassiana and the experiments were arranged in a Completely Randomized Design for the laboratory experiment and Randomized Complete Block Design for the screen house trial. Two hundred microns of three level dilutions (101, 103 and 105) of the ten isolates of fungi that had been identified using morphological and molecular tools were tried on the second, third and fourth instar larvae of the fall armyworm in a 12cm diameter feeding chamber to determine the potency of the fungus to immobilize and kill the larvae based on daily mortality checks for the laboratory analysis while for the screen house, the second instar larvae treated with the ten isolates of the Beauveria bassiana at concentration levels 101, 103 and 105 were introduced into the whorl of individual stand of four week old maize planted in rows of ten plants and observed for damage over a period of seven days and rated using IITA visual rating scales for leaf damage assessment. The experiments were replicated three times and data collected were analyzed using SPSS 2.0 at 5% level of significance. All the isolates were very potent against the larvae of the FAW at higher concentrations and lower dilutions for both experiments.