L33 may refer to:

• CITER 155mm L33 Gun, an Argentinian artillery field gun
• HMS L33, a 1917 British L class submarine
• L33, aka LZ76, a 1916 German Zeppelin

• Psilocybe mexicana
• Psilocybes
• Psilocybe semilanceata
• Psilocybe tampanensis
• Psilocybe weilii
• Psilocybin
• Psilocybin mushroom
• Psilomelane
• Psilon pneuma
• Psilophyta
• Psilops paeminosus
• Psi-Lord
• Psiloritis
• Psilostachys
• Psilotaceae
• Psilotales
• Psilotophyte
• Psilotum
• P.S. I Love You (Beatles song)
• Psiloxylaceae
• Psiloxylon
• PSINet
• PSINet Stadium
• Psiolomelane
• Psion (comics)