This research investigated the design, chemical modification, characterization and biocidal evaluation of waxes. Tallow (animal fat), bee-wax (insect) and shea butter (plant fat) were first converted to carboxylates by metathesis and later transformed into urea and thiourea complexes. The transformation was monitored using UV–visible, FT-IR and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy. They were also screened for biocidal activities using two white rots (Pleurotus sajor-cajor and Pleurotus oestratus), two brown rots (Sclerotium rolfsii and Rhizotonia solanii) and a soft rot (Cheatomium globosum). The UV–visible absorption peaks shifted to a longer wavelength for the complexes in relation to the carboxylates signifying lower energy and higher activities. Carboxylates showed very sharp peaks around 1700 cm−1 attributable to the carbonyl functional group (C=O) (Scheme 1), the carbonyl (C=O) peaks in the carboxylates were replaced by the appearance of another peaks in the urea and thiourea complexes at around 1600 cm−1 attributable to azomethine (C=N) (Scheme 2 and 3). None of the surface morphologies of the samples (crystalline) is identical. This result further confirmed the formation of the products. The result of fungi assay showed that tallow based carboxylate, urea and thiourea complexes greatly inhibited the growth of all the fungi species used. However, bees wax based carboxylate and its complexes as well as plant-fat based carboxylate and its complexes could not inhibit the growth of Sclerotium rolfsii. For insect and plant-based urea complexes, there were tiny growths (pin head) seen on the plates inoculated with P. sajor-cajor and P. oestratus, respectively. The findings of this work showed that urea and thiourea complexes performed better than carboxylates in fungi inhibition. Tallow-based products (carboxylates, urea and thiourea) showed the greatest anti-fungi properties.