Police said the orange-robed novice had been arrested after the 39-year-old unnamed British woman told police he had attacked her at a tourist site in the north-west of the country.
Cambodian monks at the historic temples of Angkor Wat (file picture). A monk has been arrested on suspicion of raping a British tourist in the north of the country
Police chief inspector Mey Chhengly said details of the sexual attack were still sketchy.
The British woman had gone alone to the summit of the Phnom Sam Pov mountain where there is a temple and three natural springs.
According to the inspector, the monk had befriended the woman when she arrived to look around the area.
He added that she and Sophoan, who had joined a temple only one month earlier, were still giving their sides of the incident.
'He admitted to the rape as soon as we arrested him,' said Chhengly.
The inspector continued that when senior monks heard about the alleged attack, Shophoan was defrocked immediately.
The monk faces up to 25 years in jail if he is convicted of rape.
Many young Cambodians become monks to escape widespread poverty, but they do not always devote their lives to the clergy.
Sometimes they are briefly ordained so they can pay gratitude to their parents, honour a dead relative or study Buddhism.
They are a common sight on the streets of most towns as they walk around carrying pots to collect alms to pay for their temple food.
Cambodia is becoming increasing popular with Western tourists, although officials advise it is still a 'risky' country, where robberies are common.
Last month four men, former members of Pol Pot's Khmer Rouge guerrillas, received lengthy jail sentences for the murder of British mine expert, 37-year-old Christopher Howes.
Last January an eight-year-old French girl was molested by a monk at the famous Angkor Wat ruins and he was instantly defrocked.
Seven months later a monk was arrested after being accused of the rape and murder of a Cambodian child, aged 10.