Boris I is quite active in inculcating the Christian faith among the Bulgarian people, in organizing the Bulgarian church as an independent institution, and in building churches throughout the country.

In 886, he gives asylum to Clement, Nahum, and Angelarius, the disciples of Cyril and Methodius, missionaries to the Slavs, who had been driven out of Moravia by the Frankish clerics.

The Glagolitic alphabet, devised by Cyril and Methodius, is adopted in the Bulgarian Empire.