For All the Saints
- Short biography of Pope St. Sixtus I.
- http://www.saintpatrickdc.org/ss/0403.htm#sixt

The Ecole Glossary
- Brief article on Pope St. Sixtus I, by Karen Rae Keck.
- http://www2.evansville.edu/ecoleweb/glossary/sixtusi.html

Catholic Encyclopedia
- Pope St. Sixtus I. Also spelled Xystus. Martyr, reigned for ten years in the very early part of the second century.
- http://www.newadvent.org/cathen/14031b.htm

Popes Through the Ages
- Profile of St. Sixtus I, from the book by Joseph Brusher.
- http://www.cfpeople.org/Books/Pope/POPEp7.htm