The present invention pertains to a composition for treating joint diseases and a kit including the same, and the purpose of the present invention is to provide a composition for treating joint diseases which can be used in patients with joint diseases, and a kit which includes the same. Specifically provided is a composition for treating joint diseases that obtains higher efficacy than prior preparations by means of a composition for treating joint diseases which includes a modified hyaluronic acid having a group derived from an anti-inflammatory compound or a pharmaceutically acceptable salt of the modified hyaluronic acid, and which is targeted at patients with human joint diseases who have a BMI of 25 kg/m2 or higher.