The street fight was the culmination of years of antagonism between monks from the two temples who had often exchanged curses, insults and rude gestures as they collected alms on different sides of a road, the Manager newspaper said.
"When an ordinary person is given a middle-finger sign, he will be mad. So am I," it quoted one of the defrocked monks, Boonlert Boonpan, as saying after the brawl in the northeastern state of Nong Khai on Monday.
Boonlert said he usually carried a knuckle-duster in his shoulder bag during the morning collection of alms on which Bhuddist monks depend, it said.
Boonlert and the four other monks, all aged between 15 and 28, were each fined 1000 baht ($NZ35) by police for public brawling and were defrocked by senior monks, Wut Pomraksa, head of Nong Khai police station, told Reuters.
Boonlert was unrepentant.
"If senators can fight in parliament, why can't monks?" he said.