He married Mary Billings Hinckley on July 18, 1888 at Beach Bluff, Massachusetts. She was descended from Thomas Hinckley, the last governor of Plymouth Colony. Professor Lanman spent his sabbatical year with his new wife in India on a one-year honeymoon. As he travelled across India in 1889 he bought for Harvard University some 500 Sanskrit and Prakrit books and manuscripts, which, with those subsequently bequeathed to the university by Fitzedward Hall, make the most valuable collection of its kind in America, and made possible the "Harvard Oriental Series", edited by Lanman.