An inbred sunflower line, designated PHA305, the plants and seeds of inbred sunflower line PHA305, methods for producing a sunflower plant either inbred or hybrid, produced by crossing the inbred sunflower line PHA305 with itself or with another sunflower plant, and hybrid sunflower seeds and plants produced by crossing the inbred line PHA305 with another sunflower line or plants and to methods for producing a sunflower plant containing in its genetic material one or more transgenes and to the transgenic sunflower plants produced by that method. This invention also relates to inbred sunflower lines derived from the inbred sunflower line PHA305, to methods for producing other inbred sunflower lines derived from inbred sunflower line PHA305, and to the inbred sunflower lines derived by the use of those methods.