The 51-year-old "Zombieland" actor has invested in the Prairie Pulp & Paper Inc company, which uses a wheat-straw waste and wood fibre alternative to tree pulp to make paper, reported Contactmusic.
"The new paper is going to be great for our future," said Harrelson.
The actor claimed that by replacing two packs of traditional paper with his product users will save one tree. The line will be sold in the US through retailer Staples.