Most of the injured are prisoners who were shot by guards. Police deny claims that three inmates were killed.
Several buildings were set alight in the remand wing of Colombo’s main prison before order was restored.
Prisoners say they want better food and conditions. Police said inmates were angry at moves to curb drug smuggling.
The head of Sri Lanka’s prisons department admitted that the treatment of prisoners in the jail fell short of acceptable standards.
A local resident told the Associated Press news agency that disturbances had been going on for several days.
Throughout Tuesday smoke billowed from the Welikada (Magazine) prison as dozens of inmates demonstrated on the rooftops. Some held up a banner calling for the head of the prison to be removed.
The BBC’s Charles Haviland says the air outside the jail was acrid with tear gas and smoke – inside the barrier gate the prison is teeming with police and armed military.