John William Ditter Sr. (September 5, 1888 – November 21, 1943) was a Republican member of the U.S. House of Representatives from Pennsylvania.

John William Ditter Sr. was born in Philadelphia, Pennsylvania on September 5, 1888.

He worked as a professor of history and commerce in Philadelphia high schools from 1912 to 1925.

Ditter was elected as a Republican to the Seventy-third from the 17th District of Pennsylvania and to the five succeeding Congresses.

During his years in Washington, Ditter served on the House Committee on Appropriations.