"I have decided to donate my body and all my organs to charity. When you receive my message, I will already be dead. Sorry for bothering you," the message to police read according to the official Xinhua news agency.
The man, surnamed Wang, was later found hanging from an air conditioning unit outside his house in Hangzhou, in the eastern province of Zhejiang, it reported.
Wang, 30, suffered from muscular dystrophy, police said. A wheelchair was found by his side with a walking stick and two notes.
He felt he had suffered enough, but wanted to make a final contribution to society, Xinhua said.
"My last and biggest wish is to donate all my useful organs and body to charity. I hope you respect my choice," it cited one of the notes as reading.
But the local branch of the Chinese Red Cross refused to accept the donation as Wang had not applied in advance or taken the necessary check-up, Xinhua added.
China has a chronic shortage of organ donors and still uses organs from executed prisoners in transplants, despite repeatedly pledging to begin phasing out the controversial practice.