Bristol's players celebrate their dramatic win at the final whistle
Bristol: (11) 14
Drop-goals: Hill, Strange
Gloucester (9) 12
Pen: Walker 4
Jason Strange's drop-goal with the last kick of the match took Bristol back to the top of the Premiership table.
Gloucester to looked to have won thanks to Willie Walker's 75th-minute penalty, but Bristol went through 17 phases to provide Strange with his chance.
Mark Regan's try and two David Hill kicks gave Bristol an 11-9 lead at the break in horrendous weather conditions.
The match became a war of attrition, but Strange handed Gloucester their first Premiership defeat of the season.
Driving rain and strong winds made life difficult for both sets of players, but it was Gloucester who made the most mistakes early on.
Brian O'Riordan's clever box kick into space was regathered by Bristol, and the ball found its way to Regan, lurking on the left wing, to burst through two tackles and score in the corner.
Bristol continued to play the conditions better than their opponents, sticking to executing the basics well.
Peter Buxton drives forward for Gloucester in a bruising encounter
Hill, whose kicking from hand kept the pressure on the visitors, slotted a penalty to keep the scoreboard ticking over for Bristol.
A superb outside break from centre Anthony Allen gave Gloucester fans something to cheer, although the move ended with a knock-on.
That seemed to spark Gloucester, and Walker kicked a penalty after Bristol strayed offside in midfield following a prolonged spell of pressure.
A smartly taken drop-goal from Hill restored Bristol's eight-point lead but a yellow card for his team-mate Ron Higgitt, for not rolling away at the tackle, prompted a Gloucester revival.
Walker kicked two penalties in the last five minutes of the half to bring the teams into the interval just two points apart.
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Gloucester's kicking game was much sharper in the early stages of the second half and their spirits were further boosted by a missed Hill penalty.
Both sides were content to rely on opposition errors, although a superb break from Bristol's outstanding number eight Dan Ward-Smith gained 60m for his side.
Gloucester set up camp in Bristol's 22m for long periods but could not make their territorial dominance tell until Walker's well-struck late penalty.
But Bristol refused to panic, and they went through phase after phase to take Strange into drop-goal range and the substitute slotted it nervelessly.
Bristol coach Richard Hill on the performances of Jason Strange and Dan Ward-Smith:
"Jason has taken a big disappointment with David Hill coming in, given that he had been our top dog at fly-half for two years.
"I am delighted for him. It was a superb achievement to land that kick under such pressure, and it showed great character.
"And Dan has got star quality, and from talking to (England head coach) Andy Robinson I know he is being looked at very carefully.
"He is developing very well, and I believe his time could come."
Gloucester head coach Dean Ryan:
"We got ourselves into a position to win the game, but you have to give credit to Bristol.
"We spent the best part of 87 minutes away from home in awful weather getting ourselves into a position to win the game, so we cannot allow a late drop-goal to instigate our reaction."
Bristol: C Morgan; Robinson, Brew, Higgitt, Lemi; Hill, O'Riordan; Hilton, Regan, Crompton, Winters, Llewellyn (capt), Budgett, El Abd, Ward-Smith.
Replacements: Blaney, Clarke, Sambucetti, To'oala, Nicholls, Strange, Taumalolo.
Gloucester: Morgan; Bailey, Tindall, Allen, Simpson-Daniel; Walker, Thomas; Wood, Azam, Califano, Eustace, Brown, Buxton (capt), Boer, Narraway.
Replacements: Elloway, Forster, Collazo, Pendlebury, Balding, Adams, B Davies.