I have to believe that it's leather as it seems to be a genuine Levy's strap and it's stamped as leather, but it doesn't look or feel like any leather I've seen before - very smooth (like zero grain/texture) and stiff. Other than that it works well and is comfortable enough.
I have another Levys strap which I use on one of my Les Pauls to great effect. That is what prompted me to get another. The strap itself if very well made but shorter by 3-4 inches from my other one. This means that even at maximum length my Les Paul rides several inches higher than I really like. In future I will ask for the length to double check.