Robson reaching the second round of last week's Shenzhen Open proved enough for her to climb from 53rd to 50th in the new WTA ranking list published on Monday.
The teenager, beaten in the first round in Hobart on Sunday, joins Heather Watson in the top 50. Watson also climbs to a career-high of 47th in the new list.
Both are due to compete in next week's Australian Open, although Watson is currently nursing an elbow injury.
The last time Britain had two players in the top 50 was back in July 1987 when Jo Durie and Sara Gomer both occupied slots in the elite.