- May 1 Admiral Paul Koundouriotis becomes President of Greece
Historic Event
May 1 German automobile manufacturers Daimler-Motoren-Gesellschaft and Benz & Cie begin their first joint venture (later merge into Mercedes-Benz)
- May 2 Netherlands refuses to recognize USSR
- May 3 Aleph Zadik Aleph is formed in Omaha, Nebraska by Sam Beber
- May 4 VIII Summer Olympic Games open at Olympic Stadium of Colombes, Paris, France
- May 4 German Republic election: fascists & communists win
- May 5 Unions terminate Twentse textile strike
- May 7 Peruvian Torre forms APRA, Alianza Popular Revolutionaria Americana
Music History
May 8 Arthur Honegger's orchestral tribute to steam locomotives "Pacifica 231" premieres
Appointment of Interest
May 10 J. Edgar Hoover appointed head of FBI
- May 11 Cartel des Gauches wins French parliamentary election
Historic Event
May 11 Pulitzer Prize awarded to Robert Frost (New Hampshire)
- May 12 49th Preakness: John Merimee aboard Nellie Morse wins in 1:57.2
- May 16 108°F (42°C) in Blitzen, Oregon
- May 17 50th Kentucky Derby: John Mooney aboard Black Gold wins in 2:05.2
- May 21 Nathan Leopold & Richard Loeb kidnap and kill Bobby Franks to demonstrate their supposed intellectual superiority by committing a "perfect crime"
Historic Event
May 26 US President Calvin Coolidge signs Immigration law restricting immigration
- May 29 AEK Athens FC is established on the anniversary of the siege of Constantinople by the Turks
- May 30 Socialist Matteotti falls in Italian parliament by fascists
- May 30 Indianapolis 500: Lora Lawrence Corum starts the race and is relieved midway by Joe Boyer who drives to victory; both drivers credited as "co-winners"
- May 31 China recognizes the USSR