PROBLEM TO BE SOLVED: To provide a method capable of selecting in superior accuracy, even in the case of a tree seed which is difficult to be selected between a nondefective seed and a defective seed, without combining a plurality of selection methods with sacrifice of a yield.SOLUTION: Seeds are inputted into an aqueous solution containing polyethylene glycol, and the seeds are selected by difference of sink-and-float. In this case, as the concentration of polyethylene glycol, a range of 6 wt% to 40 wt% is preferable. Further, it is preferable that the seeds are inputted into the aqueous solution and stirred for a prescribed time, from the viewpoint for heightening efficiency and accuracy of selection of the seeds.
