It is the latest in a series of similar incidents, with Edinburgh’s public transport services subject to multiple attacks by groups of youths in recent weeks.
No injuries were reported in the latest incident, but police are trying to trace those involved.
A spokesperson for Police Scotland said: “We received a report regarding a service bus window being smashed at the junction of Wishaw Terrace and London Road in Edinburgh at around 5.58pm on Sunday, 2 May, 2021.
“Nobody was injured in the incident and enquiries are at an early stage.”
An eyewitness said: “I was one of four people upstairs, and what a fright – so be careful guys.
“We were all thankful none of us chose those seats.”
A spate of antisocial behaviour saw Lothian Buses cancel all of their services after 7pm back in March.
One incident saw a bus driver being injured in Niddrie when the front window was smashed.
The trams have also been affected after police investigated an incident where a window was smashed near the Saughton tram stop in March.
Officers have been patrolling on buses, in vehicles, and on foot in areas affected and have identified and charged several young people.
Police have also engaged with more than young people to ensure relevant safety and prevention messaging is delivered.
Other measures have included visits to parents of youths identified as being involved and warning letters issued.