SMX may refer to:

As an abbreviation:

• SMX (operating system), a Unix-like simulator on SPARC, the "SunOS/Solaris MINIX"
• Standard Musical Expression, a representation of simple music in ASCII that was used in some DOS software such as QBasic
• SMX Convention Center (company), an events venue management company in the Philippines
  • SMX Convention Center Manila, Pasay, Philippines
• Sulfamethoxazole, an antibiotic
• Honda S-MX, a minivan
• Spatial multiplexing, MIMO wireless transmission technique
• Singapore Mercantile Exchange
• SmX RNA and SmY RNA, ribonucleic acids in nematode worms
• S.M.X., director of Revelation at the 1999 New York Underground Film Festival
• StepManiaX, a rhythm game by Step Revolution

As a code:

• Santa Maria Public Airport, in California, US, IATA code
• C.A.I. First, regional Italian airline, ICAO airline code
• SMTC Corporation, Canada, TSX/Toronto ticker code
• Sanmenxia city in Henan, China, governmental code SMX
• Sendmail X, now MeTA1, mail server coded smX
• Special Mobile Machine—Exempt, prefix SMX, on vehicle registration plates of Colorado