Structural, molecular and functional changes were also seen in their brains.
Writing in the journal Nature Medicine, the US team led by Dr Tony Wyss-Coray, from Stanford University, said: "Our data indicate that exposure of aged mice to young blood late in life is capable of rejuvenating synaptic plasticity and improving cognitive function.
"Future studies are warranted in aged humans and potentially those suffering from age-related neurodegenerative disorders."
Evidence was seen of new connections forming in the hippocampus, a brain region vital to memory and sensitive to ageing.
Dendritic spines - finger-like extensions from the branches of neurons that are thought to play a role in memory formation - also became more dense.
Ageing mice given eight infusions of young blood over three weeks improved their performance in mental tests of fear condition and locating a hidden platform in a water maze.
Infusions of blood from other elderly mice had no effect.
What caused the changes is still unknown, but it appears to involve activation of a protein called Creb in the hippocampus that helps regulate certain genes.
