Henman, ranked at No 2 in Britain behind Greg Rusedski, overtook the Spaniard, Alex Corretja, after gaining 127 ranking points with his semi- final appearance in the Du Maurier Open in Toronto, Canada, last week.
Corretja, who did not play last week, lost 16 points - and it was enough to send him four points below Henman, who now has 2,290 points.
Henman's recent form has also given him a chance of gaining a place in the ATP Tour finals in Hanover, Germany, in November. The top eight players, ranked only on their 1998 form, make the finals - and Henman is currently in 10th spot.
Rusedski, who has not played since Wimbledon because of a severe ankle injury, is still ranked sixth in the world. He had been hoping to compete in the Cincinnati tournament in the United States, which started yesterday, but he is giving his ankle one more week to recover and now plans to return at the Indianapolis tournament next week.
Henman, meanwhile, has been seeded 11th in Cincinnati, an event which includes all the world's top 12, with the exception of Rusedski, in the singles draw.
The Oxford player has drawn the Austrian left-hander Thomas Muster, once the world No 1 but now at No 24, in the first round and could face the Australian Patrick Rafter, who beat him 6-2, 6-4 in Toronto, in the third round.
Chris Wilkinson, the British No 3, has gone down from 124 to 127, and Britain's No 4 Andrew Richardson has dropped from 189 to 196.
Sam Smith, the top British woman, moved to her highest ever world ranking of 56 from 59 even though she did not compete anywhere last week. She moved up three places because other women lost points.Reuse content