The monk, who heads a temple in the coastal town of Matara, 130 kilometers (80 miles) south of Colombo, allegedly abused the 15-year-old girl over a period of time, said Dimutu Galappatti, spokesman for the National Child Protection Authority.
The monk was arrested on Sunday by a special police unit attached to the authority as a result of a tip-off, he said.
Several pornographic videotapes and contraceptives were found in the monk's possession at the temple, Galappatti said.
He said three teams were investigating the incident and further details were not immediately available.
Sri Lanka's saffron-robed monks are a powerful group in the Buddhist-majority country and play a major role in molding the island's political and social fabric.
In 2003, two Buddhist monks and eight other men were arrested and accused of sexually abusing 11 children orphaned by the island's two-decade civil war.
Child abuse in Sri Lanka is a non-bailable offense and with a maximum 10-year prison sentence.