- May 1 World's most intense shower (2.47" in 3 minutes) at Portobelo, Panama
- May 2 1908 "Take me out to the Ball Game" registered for copyright.
- May 5 34th Kentucky Derby: Arthur Pickens on Stone Street wins in 2:15.2
Event of Interest
May 12 George Bernard Shaw's "Getting Married" premieres in London
George Bernard Shaw
- May 12 Wireless Radio Broadcasting is patented by Nathan B Stubblefield
- May 14 1st passenger flight in an airplane
- May 15 Reich Association Law comes into force
- May 21 1st horror movie (Dr Jekyll & Mr Hyde) premieres in Chicago
- May 21 Bill Burns pitching for Washington Senators has no-hitter broken up with 2 outs in 9th
- May 23 Dirigible explodes over San Francisco Bay, 16 passengers fall, none killed
- May 23 Part of Great White Fleet arrives in Puget Sound, Washington
- May 24 Belgium Catholic socialist/liberal parliamentary election
- May 24 John Masefields "Tragedy of Nan" premieres in London
- May 26 At Masjed Soleyman (مسجد سليمان) in southwest Persia, the first major commercial oil strike in the Middle East is made, rights acquired by the United Kingdom
- May 27 Maulana Hakeem Noor-ud-Din iss elected the first Khalifa of Ahmadiyya Muslim Community.
- May 30 1st federal workmen's compensation law approved
- May 30 42nd Belmont: Joe Notter aboard Colin win
- May 30 Aldrich Vineland Currency Act forerunner to Federal Reserve System
- May 30 Paris advocate E Archdeacon is 1st passenger in a airplane
- May 30 US Assay Office in Salt Lake City, Utah authorized
- May 31 Miss Pottelsberghe de la Pottery is 1st airplane passenger (Belgium)