He now faces a ban from all athletics for two years and under British Olympic Committee rules may never be allowed to run in the Olympics again.
The test he took in August showed he had a banned steroid called THG in his body, which builds bigger muscles and helps athletes train harder.
Chambers, 25, says he didn't take the steroid on purpose.
Drugs tests are split into two, and if the A sample is positive, then the B sample is tested too.
That's what's happened to Chambers, and now his B sample has shown THG as well, he's been suspended.
Chamber's last chance is a disciplinary hearing, but if he is found guilty then, his ban will start.
If Chambers is found guilty, Britain will lose its silver medal from the 400-metre relay at the World Championships in Paris in August. Chambers ran the last leg in the final.