Donald C. Rosinski, 53, a native Washingtonian and a specialist in downtown commercial property leasing, died Wednesday following a heart attack while en route to a business appointment. A member of the family said he had been in excellent health.

After growing up in the Chevy Chase area of Washington and graduating from Gonzaga High School and George Washington University with a law degree, Mr. Rosinski was admitted to the practice of law. Later he joined Carl C. Rosinski Co., a realty firm founded by his father. In recent years Mr. Rosinski had headed the firm, which specializes in commercial property sales and leasing.

In the early 1960s, Mr. Rosinski was given the Martin Isen award from the Washington Board of Realtors for high ethics and professionalism. He was named "outstanding young Washingtonian of the year" in 1965 by the downtown chapter of the D.C. Chamber of Commerce. Last year, he was commended by the Washington realtors board for outstanding service to the community. He had served several terms as a WBR director.

Mr. Rosinski also was active with the Washington Metropolitan Board of Trade, serving on the zoning and parking committees and as a director.

In addition, Mr. Rosinski was on theboardsof directors of American Federal Savings & Loan Association, the Equitable Life Assurance Society and Columbia Title Insurance Co.

He was a past president of the Holy Name Society of Our Lady of Mercy Catholic Church in Bethesda and had served as chairman of a campaign of the Archdiocese of Washington to aid needy people.

He was a member of the Bethesda Country Club, where he played tennis.

Surviving are his wife Frederika, of the home in Bethesda; three daughters; Mary Morey of Austin, Tex., and Catherine and Jane, of the home; a son, Stephen, also of the home; two sisters, Anne Redman of Washington, and Joan M. Eccard of Silver Spring, and a grandchild.