Goals from strikers Adam Armstrong and Sam Winnall ensured Barnsley got their first win in seven games.
The frontmen struck in either half to condemn Brentford to their first home loss of the campaign.
Defender Marc Roberts was not named in the squad after failing to recover from an injury picked up in Tuesday night's defeat to Newcastle United and he was replaced by Angus MacDonald.
Adam Hammill was named as a substitute alongside young striker Jacob Brown with Tom Bradshaw also missing out.
Marley Watkins moved to the left wing whilst Armstrong partnered Winnall up front.
Armstrong was the first Barnsley player to have a sight of goal but his 25-yard effort dribbled harmlessly wide.
Winnall then volleyed wide from Watkins' cross and Ryan Kent fired straight at Brentford 'keeper Daniel Bentley from the edge of the area.
Winnall had another effort go wide moments later after he cleverly wriggled free from two challenges in the box.
The home side then missed a glaring chance to go in front, Scott Hogan, once a trialist at Oakwell, got clear down the right and squared for Sully Kaikai who scooped his shot over from close-range.
Armstrong then struck the opener after seizing on a loose ball in the box and beating Bentley.
Andy Yiadom then had to clear acrobatically from a cross into the box but his clearance fell to Ryan Woods who tested Adam Davies with a driven shot.
Brentford continued to carve out opportunities to get level with Nico Yennaris dragging an effort wide from Kaikai's free kick and Sam Saunders' heading just over the bar.
Barnsley started the second half in a lively manner with James Bree firing wide from distance and then Kent and Watkins having efforts on goal.
MacDonald also headed over from Conor Hourihane's free kick.
They made it two on 67 minutes when Kent played a neat one, two with Armstrong and then fired against the post. The ball fell kindly to Winnall who could not miss from close-range.
Davies then denied Brentford sub Josh Clarke with a brave block and tipped over from Yennaris as Barnsley saw out the game with a clean sheet.
Brentford: Bentley, Colin, Bjelland, Egan, Barbet, Yennaris, Woods, Saunders (Clarke half time), Sawyers (Hofman 78), Kaikai (McEachran 58), Hogan.Unused: Bonham, MacLeod, Dean, Kerschbaumer.
Barnsley: Davies, Bree, MacDonald, Jackson, Yiadom, Kent (Hammill 86) Morsy, Hourihane, Watkins, Winnall (Brown 90+2), Armstrong (Williams 85).Unused: Townsend, Kpekawa, Evans, Lee, Brown.
Referee: James Linington (Isle of Wight).
