The Hollenfelz House, also known as St. Mary's High School for Boys, is a historic building located in Dubuque, Iowa, United States.

This highly decorative Second Empire structure was built as a home for Michael Hollenfelz, who owned a wholesale firm dealing with wines, liquors and beer.

The building features a mansard roof with dormers and a cupola, which is normal for this style, and High Victorian decorative details, which is not.

The school was operated by the Brothers of Mary from St. Louis, and its curriculum focused on business and commerce.

This article about a property in Dubuque County, Iowa on the National Register of Historic Places is a stub.