Harold Charles Ostertag (June 22, 1896 – May 2, 1985) was an American politician, a United States Representative for the 41st, 39th, and 37th Congressional Districts of New York.

He worked for the New York Central Railroad from 1917 to 1950 and became assistant to the vice president of the traffic department.

During World War I, Ostertag enlisted in the New York Army National Guard's 74th Infantry Regiment.

Ostertag, who had attained the rank of Sergeant, completed officer training and received his commission as a Second Lieutenant while serving with the 55th in France.

Ostertag's wife Grace was Grand Matron of the Order of the Eastern Star and first vice president of the Congressional Club.