Scrumhalf Paul Marshall grabbed a brace of tries, and wing Andrew Trimble also crossed the whitewash at Ravenhill in Belfast as last season's runners-up began their new European Cup campaign on a winning note
Paddy Jackson converted three of the tries and added five penalties for Ulster, who were soundly beaten 42-14 by fellow Irish side Leinster in last season's final.
Ulster, the 1999 European champions, are now unbeaten in six matches this season.
In the night's other game on the opening night of the tournament, Welsh side Ospreys also secured a bonus point victory over Italian side Treviso with a last-minute try from inside centre Ashley Beck.
Eli Walker and Hanno Dirksen, with a brace, scored tries, with flyhalf Dan Biggar kicking 18 points at Swansea's Liberty Stadium. Treviso scored two tries through Manoa Vosawai and Luke McLean.
"We are pretty pleased with the performance, but there's still a bit to work on. We have got to be able to think a bit quicker and not play so wide too early," said Ospreys captain Alun Wyn Jones.
"We can be pleased with the end result and the most pleasing thing for me was the composure we showed in the last minute, minute and a half.
"In the past you would have seen us tighten up in that situation but we realise that these pool games will come down to the last minute."
The win was sweet revenge for Ospreys, who had lost 12-6 to the same opponents in the Celtic League earlier this season.
All the teams and scorers:
Ulster 41-17 Castres
The scorers:
For Ulster:
Tries: Trimble, Marshall 2, Pienaar
Cons: Jackson 3
Pens: Jackson 5
Castres:
Tries: Andreu, Garvey
Cons: Teulet 2
Pen: Teulet
Teams:
Ulster: 15 Jared Payne, 14 Tommy Bowe, 13 Darren Cave, 12 Paddy Wallace, 11 Andrew Trimble, 10 Patrick Jackson, 9 Paul Marshall, 8 Stephen Ferris, 7 Chris Henry, 6 Iain Henderson, 5 Dan Tuohy, 4 Johann Muller (captain), 3 John Afoa, 2 Rory Best, 1 Tom Court.
Replacements: 16 Rob Herring, 17 Callum Black, 18 Adam Macklin, 19 Lewis Stevenson, 20 Mike McComish, 21 Ruan Pienaar, 22 Luke Marshall, 23 Craig Gilroy.
Castres: 15 Romain Teulet, 14 Marcel Garvey, 13 Seremaia Bai, 12 Daniel Kirkpatrick, 11 Marc Andreu, 10 Pierre Bernard, 9 Thierry Lacrampe, 8 Pedrie Wannenburg, 7 Yannick Caballero, 6 Piula Faasalele, 5 Rodrigo Capo Ortega, 4 Matthias Rolland (captain), 3 Michael Coetzee, 2 Mathieu Bonello, 1 Yannick Forestier.
Replacements: 16 Marc-Antoine Rallier, 17 Gregory Marmoiton, 18 Hai Lazar, 19 Joe Tekori, 20 Antonie Claassen, 21 Rory Kockott, 22 Paul Bonnefond, 23 Thomas Sanchou.
Referee: Andrew Small (England)
Assistant referees: Martin Fox (England) , Stuart Terheege (England)
TMO: Geoff Warren (England)
Ospreys 38-17 Treviso
The scorers:
For Ospreys:
Tries: Walker, Dirksen 2, Beck
Cons: Biggar
Pens: Biggar 4
For Treviso:
Tries: Vosawai, McLean
Cons: Burton
Pen: Burton
Teams:
Ospreys: 15 Richard Fussell, 14 Hanno Dirksen, 13 Andrew Bishop, 12 Ashley Beck, 11 Eli Walker, 10 Dan Biggar, 9 Kahn Fotuali'I, 8 Jonathan Thomas, 7 Justin Tipuric, 6 Ryan Jones, 5 Ian Evans, 4 Alun Wyn Jones (captain), 3 Adam Jones, 2 Richard Hibbard, 1 Ryan Bevington.
Replacements: 16 Matthew Dwyer, 17 Duncan Jones, 18 Aaron Jarvis, 19 George Stowers, 20 Sam Lewis, 21 Rhys Webb, 22 Matthew Morgan, 23 Thomas Isaacs.
Treviso: 15 Luke McLean, 14 Ludovico Nitoglia, 13 Tommaso Benvenuti, 12 Alberto Sgarbi, 11 Tommaso Iannone, 10 Kristopher Burton, 9 Tobie Botes, 8 Manoa Vosawai, 7 Alessandro Zanni, 6 Simone Favaro, 5 Valerio Bernabo, 4 Antonio Pavanello (captain), 3 Bees Roux, 2 Leonardo Ghiraldini, 1 Alberto De Marchi.
Replacements: 16 Enrico Ceccato, 17 Ignacio Fernandez-Rouyet, 18 Pedro Di Santo, 19 Francesco Minto, 20 Paul Derbyshire, 21 Robert Barbieri, 22 Fabio Semenzato, 23 Andrea Pratichett.
Referee: Neil Paterson (Scotland)
Assistant referees: David Changleng (Scotland), Bob Nevins (Scotland)
TMO: Jim Yuille (Scotland)
Source: Rugby365
