The invention relates to the soybean variety designated D4120384. Provided by the invention are the seeds, plants and derivatives of the soybean variety D4120384. Also provided by the invention are tissue cultures of the soybean variety D4120384 and the plants regenerated therefrom. Still further provided by the invention are methods for producing soybean plants by crossing the soybean variety D4120384 with itself or another soybean variety and plants produced by such methods.