Lieutenant General Jagath Jayasuriya, 50, said his first priority would be the military's new role in supporting a massive reconstruction effort in areas once held by Tiger separatists.
"We have to transform them from fighting to other things," he said at the tightly guarded army headquarters here.
"We have to re-motivate them."
"Running a peacetime army is quite different. Discipline has to be emphasised.
I am very concerned about it," he said.
Government forces declared victory over Tamil Tiger rebels in March after wiping out the entire leadership of the Liberation Tigers of Tamil Eelam (LTTE), which took up arms in 1972 to fight for a separate Tamil homeland.
The new chief said the army had recruited 80,000 soldiers in the past two years to boost its offensive against the rebels.
Jayasuriya replaced General Sarath Fonseka, who was elevated to a new post as Chief of Defence Staff with powers to map out military strategy and planning.
General Fonseka is widely seen