An elderly man with a 'Zimmer frame' type walking aid flashed at a family on the number 94 Cheltenham to Churchdown bus.
Police are now appealing for the family to get in touch with them after the incident yesterday.
The man, in his 70s, got on the bus at Montpellier last night and after sitting on a seat on the lower deck he exposed himself to the family, including children, and committed a lewd act.
It is believed the family confronted the man about his behaviour before he got off the bus at the Hare and Hounds pub on Cheltenham Road East.
The offender is described as white, in his 70s, with grey hair and wearing a black cap on his head, a camouflage three quarter length jacket, a dark cotton tracksuit and white trainers.
He was pushing a walking aid with wheels and a blue bag hanging off it.
Officers are urging the family or anyone with information about this case to call 101, quoting incident 143 of June 13.
Alternatively information can be given anonymously on 0800 555 111
