Nanocellulose　(NC)　was　prepared　from　cotton　linter　using　ionic　liquid　(IL)　1-butyl-3-methylimidazolium　hydrogen　sulfate　([Bmim]HSO4)　as　both　swelling　agent　and　catalyst　followed　by　high-pressure　homogenization.　Evidence　suggested　that　the　IL　played　a　significant　role　with　respect　to　hydrolysis　of　the　linter　cellulose.　The　effects　of　various　reaction　conditions　on　the　NC　preparation　were　investigated　in　this　study.　The　successful　conversion　of　the　cotton　to　NC　was　analyzed,　which　showed　that　the　prepared　NC　had　a　uniform　rod-like　shape　that　was　50　nm　to　100　nm　in　diameter　and　500　nm　to　800　nm　in　length.　The　characterization　of　the　NC　by　X-ray　diffraction　and　thermogravimetric　analysis　revealed　that　the　crystalline　cellulose　I　structure　was　retained　in　the　NC　and　it　showed　stable　thermal　properties.　The　recycled　ionic　liquid　exhibited　a　slightly　decreased　cellulose　hydrolysis　ability.　The　application　of　[Bmim]HSO4　as　both　a　catalyst　and　swelling　agent　introduced　an　effective　and　environmentally　friendly　method　for　NC　production.