The present disclosure provides a method for stably supplying a highly pure n-butylamine gas having a constant composition. The present disclosure is a composition supply method including: a filling step of filling a container with a composition containing n-butylamine in an amount of 99.5% by volume or more and isobutylamine in an amount of 0.001% by volume or more and 0.5% by volume or less; a warming step of warming the container filled with the composition to 50° C. or higher; and a gas supply step of supplying a gas containing n-butylamine and isobutylamine from the warmed container to a predetermined device.