Britannia Secunda was one of the provinces of Roman Britain created c. AD 312 by the Roman Emperor Diocletian.

The governors of Britannia Secunda were of equestrian rank although few are known by name. Their capital was at York.

The province probably encompassed all of what is now northern England and possibly north Wales. In 369 a new province of Valentia was created, probably from a portion of Britannia Secunda.