Controller of Immigration and Emigration Chulananda Perera said the clerics, who were mostly Pakistani, Bangladeshi, Indian, Maldivian and Arab, had travelled into the country on tourist visas.
"We have ordered them to leave the country by January 31. They have violated immigration laws. A tourist visa is to have a holiday or visit friends and family and not to preach Islam," Perera told AFP.
He said the group, which belongs to the Tabligh Jamat group, arrived in Sri Lanka last month in small batches.
Perera said he acted on several complaints by the Muslim community, that the clerics were not preaching the moderate Islam practiced on the Buddhist-dominated island.
"Foreign clerics wishing to preach Islam in Sri Lanka, must first apply for permission through the religious affairs authorities," Perera said.
In January, Sri Lanka launched an online-visa application system, scrapping the one-month visa on arrival for foreigners, except Maldivians and Singaporeans.