PROBLEM TO BE SOLVED: To enhance a seed germination suppression effect of a composition including pelargonic acid or salt thereof as a herbicidal active ingredient.SOLUTION: Provided is a seed germination suppression composition formed by adding a vegetable essential oil to a composition including pelargonic acid or salt thereof, and in which a seed germination suppression effect is synergistically enhanced. The pelargonic acid or salt thereof is included by 0.1-10 mass% and the vegetable essential oil is included by 0.0001-1 mass%, and as the vegetable essential oil, cinnamon oil, citronella oil, geranium oil, linalol, and cedar wood oil are preferable.