K31 (disambiguation)

K31 is a Swiss rifle.

K31 may also refer to:
 * K-31 (Kansas highway)
 * HMS Camellia (K31), a corvette of the Royal Navy
 * HSWMS Visby (K31), a corvette of the Swedish Navy
 * Potassium-31, an isotope of potassium
 * SOVIET SUBMARINE K-31
 * Sonata in B-flat, K. 31, by Wolfgang Amadeus Mozart