The monk, Phra Nom Panon, 67, was conducting his alms round in Pattani's Mae Lan district.
Around 6.20am, armed men dressed in military fatigues opened fire with automatic weapons as villagers approached him with offerings of food, according to local newspapers.
A policeman accompanying the monk returned fire and some of the attackers, suspected of being separatist insurgents, were wounded.
Along with the dead, six others were injured in the attack - five villagers and the policeman.
The shooting continues a spate of recent killings in Thailand's troubled south. Earlier this month, three children were shot dead by unknown assailants outside of their family home as they returned from evening prayer.
A separatist insurgency in the area has caused the death of 6,000 people - around half Muslim and half Buddhist - in the last ten years.