The Republican presidential nominee told the forum the Russian president “has been a leader far more than our president [Obama] has been”.
It came on the same day the chief of the Pentagon accused Russia of sowing the seeds of global instability.
Mrs Clinton, meanwhile, defended her judgment despite her email scandal.
The White House candidates appeared back to back on stage in half-hour segments in New York on Wednesday night.
“I think when he calls me brilliant I’ll take the compliment, ok?” added Trump.
He said Mr Putin had “great control over his country”.
The 30 minutes allotted to each candidate made the proceedings feel like the political equivalent of speed-dating.
And like speed-dating gone wrong, there was plenty of time for the participants to bury themselves with their words.
Mrs Clinton once again tripped up when discussing her use of a private email server as secretary of state.
Mr Trump found new and interesting ways to show his tenuous command of policy details and shower questionable praise on a US rival.
Written by: BBC