Footage of 15 race finishes obtained by the animal rights group and viewed by University of Sydney veterinarian Professor Paul McGreevy showed 13 occasions when the whip hit a horse's head.
The footage, which was viewed frame-by-frame, was taken over two days in June last year at Gosford racetrack, north of Sydney.
"We found that more than 75 per cent of the time the whip struck the horse in the abdomen," Professor McGreevy said on the RSPCA's website.
Australian jockeys have used padded whips since 2009 in order to reduce the impact on horses.
However, Prof McGreevy found that horses were struck with the unpadded section of the whip more than half the time.
Greens senator Lee Rhiannon said she supported a call by the RSPCA for Australia to follow the example of Norway, where whips in horseracing were banned in 1982.
She did not believe padded whips were acceptable.
"The cruelty is still considerable. Horses are feeling the pain," she told reporters in Canberra on Wednesday.
