© 2017 Elsevier Ltd After hydrodesulfurization of Mexican oil's sour acid gases, a sulfur toxic waste is recovered, we used it to synthesize cadmium sulfide quantum dots, which have been recently studied due to their optical (high photostability, high quantum yield and fluorescence) and catalytic properties. Increased demand of cadmium sulfide quantum dots has led to research of new synthesis methods that with higher yields, increased control over particle diameter, that produce hydrophilic quantum dots -as most of them are obtained in organic solvents- and that are environmentally friendly because most methods employ toxic materials or involve a high energy consumption. This study attempted to synthesize hydrophilic cadmium sulfide quantum dots using an environmentally friendly method with a fungus capable of transforming a dangerous waste into a high-value-added product. Mycelia of Fusarium oxysporum f. sp. lycopersici were incubated with 1 mM cadmium nitrate and 1% (w/v) sulfur waste at 30 °C for 24 h, then the biomass was separated through paper filtration. The filtrate became yellow indicating presence of extracellular cadmium sulfide quantum dots, as was confirmed by increased UV–vis absorption around 300 nm and fluorescence at 510 nm. The biomass of Fusarium oxysporum f. sp. lycopersici produced after 24 h, extracellular stable, hydrophilic and biocompatible cadmium sulfide quantum dots from a sulfur dangerous waste. Biosynthesized quantum dots were circular with diameter of 6.116±2.111 nm and had a wurtzite crystalline structure.