Danny Shittu's venomous 23rd-minute strike - his first goal of the season - put Rangers in the driving seat and they stayed in control until the end.
But Danny Gabbidon missed a golden chance to rescue a point for struggling Cardiff when he headed Willie Boland's cross over the bar from close range.
Cardiff City manager Lennie Lawrence:
"The real issue is their goalkeeper didn't have a shot to save.
"We played all our cards with the substitutes but we just didn't create any chances.
"We've gone from being pretty decent up front to being very poor in just three weeks and unless we do something about it we are going to be in the bottom three."
QPR: Day, Bignot, Shittu, Santos, Padula, Ainsworth, Bircham,
Gallen, Cook (McLeod 87), Cureton (Bean 88), Furlong.
Subs Not Used: Cole, Branco, Miller.
Goals: Shittu 23.
Cardiff: Warner, Williams, Gabbidon, Collins, Barker, McAnuff,
Bullock, Boland, Ledley (Jerome 63), Lee (Thorne 63), Parry.
Subs Not Used: Alexander, Weston, Vidmar.
Booked: Lee, Parry.
Ref: D Gallagher (Oxfordshire).