Petrol bombs, bottles and bricks were thrown, as republicans and loyalists clashed on the streets of Belfast.
Twenty-six police officers were injured and three hospitalised as they tried to restore order to the north of the city.
Violence erupted following a march held by the Republican Network for Unity. Organisers claim the event was targeted by loyalists in a pre-meditated strike.
Police fended off attacks from both sides and used water cannon to repel wheelie bins that had been set alight and launched at them. A number of arrests have been made.
This latest disturbance comes one week after tensions flared between the two sides when a loyalist marching band defied a ban on playing sectarian songs outside St Patrick's, one of Belfast's oldest Catholic churches.
There are fears that more violence could occur during a parade planned for September 29, when thousands of loyalists will march past the same church.
