The antimycotic effect of Casia alata (Linn.) commonly used for the treatment of skin diseases by local people in Nigeria was evaluated against dermatophytes (Trichophyton tonsurans, Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum audouinii, Microsporum canis, Microsporum gypseum, Epidermophyton floccosum). Ten-fold serially diluted extract concentrations were subjected to phytochemical screening and the antimycotic activity of the phytochemicals was evaluated via broth microdilution. The percentage yield of crude aqueous, n-hexane, chloroform, ethanol, and methanol leaf extracts of Cassia alata Linn was 5.6, 5.7, 1.6, 4.8, and 2.8%, respectively. Important phytochemicals including glycosides, anthraquinone, proteins, cardiac glycosides, steroids, alkaloids, phlabotannin, phenols, saponins, tannins, flavonoids, and carbohydrates were present in all the extracts. All the extracts inhibited the dermatophytes but at varying degrees. Similar minimum inhibitory concentration (MIC) values ranging from 1.56 to 3.125 mg/mL each for n-hexane and chloroform leaf extracts and MIC of 0.78 to 1.56 mg/mL each for ethanol and methanol leaf extracts were estimated. The minimum fungicidal concentration (MFC) of 6.25 mg/mL, 3.125 to 6.25 mg/mL, 1.56 to 6.25 mg/mL, 0.78 to 1.56 mg/mL for n-hexane, chloroform, ethanol, and methanol leaf extracts were observed and all the extracts were maximally active against E. floccosum. In conclusion, the potent anti-dermatophytic effect of the leaf extract of Casia alata Linn may be driven by their numerous phytochemicals, which justify its traditional uses for the treatment of skin diseases and could considerably illicit interest for the development of new drug leads.