Police were patrolling the area around London Bridge station just before 4.05pm on February 4.
During their patrol, a group of teenagers reportedly ran off and one of the boys was caught.
Officers carried out a stop and search which resulted in a large machete being found.
A boy was arrested on suspicion of possession of an offensive weapon.
He was taken into custody before being released on bail pending further enquiries.
A Metropolitan Police spokesperson said: “A 14-year-old boy was arrested by officers following a proactive stop and search that found he had a machete.
“Officers were patrolling the area around London Bridge Station at 16:06hrs on Tuesday, 4 February when a group of teenage boys made off from police.
“Officers apprehended one teenager and carried out a search, resulting in the discovery of the weapon.
“He was arrested on suspicion of possession of an offensive weapon and taken into custody.
“He has been bailed pending further enquiries.”