A report by the country's state media said HIV/Aids had led to the deaths of almost 7,000 people in the first nine months of 2008.
The number of deaths caused by tuberculosis and rabies fell back into second and third place.
The numbers are increasing dramatically - China's Ministry of Health say that until three years ago, fewer than 8,000 people altogether had died from HIV/Aids.
By last year, the total had risen to five times that many.
Data on HIV in China are still unreliable. Official reporting of cases does seem to have improved.
The central authorities seem more willing to recognise HIV as a public health crisis and address it with education campaigns.
But there are still concerns that officials at local and provincial level are under-reporting, either by mistake or because they think it's not in their interest to show rises.
This latest news comes as the spread of HIV in China has entered a dangerous new phase.
Initially it was concentrated in high-risk populations, injecting drug users in particular.
Infection from contaminated blood transfusions was also common. However, unsafe sex is now thought to be the main cause of transmission. Experts believe that this is caused by China's rapid social change, even though Chinese society is still deeply conservative. Migrant labour has increased and premarital sex is more common, according to reports.
