The sharp-eyed ring-tailed lemur spotted the field mouse at the Five Sisters Zoo in West Lothian.
Reaching through the cage, the lemur tried to grab the mouse, only for a keeper spot the ambush and save the mouse.
The moment was captured on camera by tourist Alasdair Preston.
The 36-year-old warehouse worker from Bathgate said: "Luckily I had my camera out ready.
"The mouse stopped just by the lemur cage to nibble on some food.
"He wasn't causing any bother but suddenly one of the lemurs clocked him.
"It looked just like the lemur wanted it a new toy or a snack and it went to pick the mouse up.
"He was just about to grab the poor mouse when a keeper spotted it, and scooped the mouse up out of harm's way. He carried it out and put him in a field.
"It was definitely a lucky escape. I'm sure the lemur wouldn't have let him go if it'd managed to get hold of him properly."