Category 3 cable, commonly known as Cat 3, is an unshielded twisted pair (UTP) cable designed to reliably carry data up to 10 Mbit/s, with a possible bandwidth of 16 MHz. It is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance and the Telecommunications Industry Association. Category 3 was a popular cabling format among computer network administrators in the early 1990s, but fell out of popularity in favor of the very similar, but higher performing, Cat 5 standard.

Now that Cat 5 is obsolete, most new structured cable installations are built with Cat 5e or Cat 6 cable. Cat 3 is currently still in use in two-line telephone systems, although Cat 5 or higher could do the same work and allow transition to VOIP.

Note that unlike Cat 1,2,4, and 5 cables, Cat 3 is still recognized by TIA/EIA-568-B, its defining standard.

Category 3 saw some extra longevity due to the 100baseT4 standard which achieved speeds of 100 Mbit/s by using all 4 pairs of wires. This allowed businesses that were already wired for Cat 3 to keep their current wiring but still upgrade to 100 Mbit/s.