It happened in front of HFD Station 51 in the 6900 block of Bellaire Boulevard near Bintliff Drive.
The firefighters were returning from a call and were backing into the fire station when the driver of an SUV crashed into the ambulance, according to Houston police.
The SUV driver was believed to have been impaired and was taken into custody, according to Houston police.
The firefighters' injuries were believed to be minor. Both were transported to a hospital as a precaution.
Station 51 houses an engine, ladder truck and an ambulance, according to Houston Fire Dept. records.