According to the invention, there is provided a novel soybean variety designated XB31W05. This invention thus relates to the seeds of soybean variety XB31W05, to the plants of soybean XB31W05 to plant parts of soybean variety XB31W05 and to methods for producing a soybean plant produced by crossing plants of the soybean variety XB31W05 with another soybean plant, using XB31W05 as either the male or the female parent.