Louw comes in on the blindside, as Guy Mercer and Simon Taylor complete the back row, while Kiwi star Donald returns to partner Michael Claassens in the half-backs.
Elsewhere, Chris Biller makes his first start for Bath, Olly Barkley and Dan Hipkiss form a new centre partnership, while Nick Abendanon returns to full-back.
European champions Leinster, who lead Bath by two points at the top of Pool 3, make a number of changes to the side that beat Glasgow Warriors in the last round.
Fergus McFadden is in at outside centre, alongside Gordon D'Arcy, while Damian Browne partners skipper Leo Cullen at second row and Richardt Strauss is named in the front row with Heinke van der Merwe and Mike Ross.
Kevin McLaughlin is alongside fellow Irish stars Jamie Heaslip and Sean O'Brien in the back row, with Isaac Boss, Gordon D'Arcy and Rob Kearney retaining their places in the starting line-up.
Bath: Abendanon; Cuthbert, Hipkiss, Barkley, Banahan; Donald, Claassens; Flatman, Biller, Wilson, Attwood, Caldwell, Louw (capt), Mercer, Taylor. Replacements: Beech, Catt, Perenise, Spencer, Beattie, Cook, Heathcote, Vesty.
Leinster: Kearney; Nacewa, McFadden, D'Arcy, Fitzgerald; Sexton, Boss; Van Der Merwe, Strauss, Ross, Cullen (capt), Browne, McLaughlin, O'Brien, Heaslip.
Replacements: Cronin, Healy, White, Toner, Jennings, Reddan, I Madigan, O'Malley.
Referee: Jerome Garces (France)
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