PURPOSE: To increase linolenic acid content in an oil extracted from soybean plant seeds and enhance functionality and nutritive value of soybean oil, by inducing mutation in soybean plants.

CONSTITUTION: Soybean plants are subjected to mutation treatment and breed the resultant soybean plants having ≥13% linolenic acid content based on the total fatty acids in fats and oils extracted from the seeds thereof. Methods for exposing soybean seeds to irradiation, varying soybean seeds with chemical mutagenic agent are cited as the applied mutation treatment. 60Co-γ Rays, 32P-β rays, X-rays are effectively used as the radiation and irradiation conditions vary with the kind of the radiation. For example, in the case of the 60Co-γ rays, exposure to radiation at 1×101W1×105R/hr is carried out for 1minW3hr. Ethylmethanesulfonic acid (EMS), nitrosoguanidine, etc., are cited as the chemical mutagenic agent. For example, in the case of the EMS, the seeds are dipped in a 0.05W0.5% solution at 4°C for 1W2hr.