The invention relates to the novel cotton variety designated STX0502RF. Provided by the invention are the seeds, plants, plant parts and derivatives of the cotton variety STX0502RF. Also provided by the invention are tissue cultures of the cotton variety STX0502RF and the plants regenerated therefrom. Still further provided by the invention are methods for producing cotton plants by crossing the cotton variety STX0502RF with itself or another cotton variety and plants produced by such methods.