For his artistic work, Sepp Mastaller was significantly influenced by the German Expressionists, especially Ernst Barlach. Mastaller's works combine unity and purposeful abstraction with spiritual expression and collected energy. Just like Ernst Barlach, Mastaller focused on the yearning for the primordial, the simple and the unconsumed.
Sepp Mastaller is one of those artists who became widely known over many years without publicising their work. More than 50 fountains, numerous architectural sculptures in public spaces, portraits and an exemplary sculptural oeuvre document the significance of this modest artist. Another proof of this is the fact that in 1968 the city of Augsburg officially awarded him with an art sponsorship.