Onychomycosis is a fairly common condition seen in a dermatology clinic. Dermatophytes Trichophyton and Epidermophyton are the known filamentous fungi implicated. The yeast-like fungi such as Candida less commonly cause Onychomycosis. The genus Prototheca may on preliminary observation resemble yeast-like fungi but a detailed microscopy will reveal the absence of budding and presence of endospores. Onychoprotothecosis is an uncommon presentation of human protothecosis. Of the two Prototheca species (Prototheca zopfii and Prototheca wickerhamii) known to cause the disease, P. wickerhamii has been reported more commonly. We report a culture proven case of this condition caused by P. zopfii. The patient, a 55-year-old housewife presented with discolouration and breaking off of the right thumb and forefinger nails since a period of six months. Samples of nail scrapping sent to the Microbiology Laboratory were culture-positive for Prototheca. Speciation by the automated Vitek-2 system (bioMerieux) identified the isolate as P. zopfii, which was further confirmed at PGI, Chandigarh.