The October 4 attack near the Mali border, thought to have been carried out by a regional affiliate of the Islamic State group, resulted in the deaths of four US soldiers and at least four Nigerien troops.
“We will look at this and say was there some things we have to adapt to,” Mattis said.
“We are not complacent, we are going to be better,” he added.
Speaking to reporters as he traveled to a military headquarters in Florida, Mattis said French aircraft were on the scene of the attack within 30 minutes.
France maintains a 4,000-man mission in the region to shore up fragile Sahel countries against jihadists who have carried out a wave of bloody bombings, shootings and kidnappings.
Some US media had questioned the efficiency of France’s air response.
“I completely reject the idea that that was slow,” Mattis said.
A French military spokesman has said his country’s helicopters had evacuated wounded and that Mirage 2000 warplanes conducted a “show of force” but did not drop any munitions to avoid hitting ground forces.
Mattis is due to visit the US military’s Central Command and Southern Command this week, both based out of Florida.