Islam spread to the Republic of the Congo from North Africa in the mid-19th century. ^[1] There is a growing Muslim community in the country, estimated at 2 percent of the population. In 2005 a large new mosque was constructed in Brazzaville. Most workers in the urban centers were immigrants from West Africa and Lebanon, with some also from North Africa. The West African immigrants arrived mostly from Mali, Benin, Togo, Mauritania, and Senegal. The Lebanese were primarily Sunni Muslims. There was also a large Chadian Muslim population.

Muslim holy days are not nationally observed; however, they are respected. Employers grant leave for those who wish to observe holy days not on the national calendar.

Source : http://en.wikipedia.org/wiki/Islam_in_the_Republic_of_the_Congo