The effect was even bigger if real, spontaneous giggles accompanied a gag, the University College London scientists said.
They tried out 40 different jokes, ranging from the groan-worthy to the hilarious, on 72 volunteers.
The findings, in Current Biology, suggest laughter might be contagious or give others permission to also laugh.
Jokes from the study included:
- Why couldn't the toilet paper cross the road? Because it got stuck in a crack.
- Why can't you give Elsa a balloon? Because she will "Let It Go".
- Why was the tomato all red? Because it saw the salad dressing.
- What's round and sounds like a trumpet? A crumpet.
- What do you call an apple that farts? A fruity tooty.
A professional comedian recorded the jokes and two versions were created, with
- staged, canned laughter
- real, spontaneous laughter
The volunteers rated only one version of each joke - but, across the study, all of the jokes were heard with both different kinds of laughter.
The addition of any type of laughter improved the "funny" rating of the jokes - even the bad ones.
But everyone in the study found jokes funniest when paired with spontaneous laughter.
Lead researcher Prof Sophie Scott said: "Historically, TV and radio programmes were always recorded in front of a live studio audience.
"This allowed those watching and listening to feel part of the performance.