- May 5 Dutch 2nd Chamber passes child labor law
- May 9 London's Victoria Embankment opens
- May 9 The first horse-drawn bus makes its début in the city of Mumbai, plying two routes
- May 12 US Assay Office in Helena, Montana, authorized
- May 13 Pope Pius IX encyclical "On Greek-Ruthenian rite"
- May 14 1st admission charge at a football game, Harvard beats Uni of McGill (Montreal) 3-0
- May 16 1st recorded dam disaster in US (Williamsburg, Massachusetts)
- May 26 2nd Preakness: William Donohue aboard Culpepper wins in 2:56.5
- May 29 Present constitution of Switzerland takes effect