Commissioner Bernard Hogan-Howe spoke out after footage emerged of one officer apparently racially abusing a man and another allegedly assaulting a teenage boy last summer.
In a statement to staff, the police chief said: "I wanted to take this opportunity to clearly and categorically reiterate that there is no place for racism in the Met."
Both incidents happened on August 11 last year as police officers in London dealt with the fallout of the riots sweeping the capital.
In an internal broadcast to staff, Mr Hogan-Howe said: "I know that the Met has changed greatly over the years, and most of you have directly been involved in improving our relationship with all Londoners and those who visit us.
"Unfortunately just one alleged incident like this can be very damaging to public confidence.
"This is a great organisation - one we should all be proud to work for. Without prejudging this case, in any instance of wrongdoing it is a small few who tarnish the vast majority.
"What we have heard over the last few days is of course completely at odds with all the close work that goes on with communities across London every day. We work hard to forge strong relationships with people who can advise us and rightly hold us to account.
"I want us all to go out there and remind those communities of our commitment to fairness and professionalism.
"We have a duty to challenge or report any behaviour by colleagues which is less than the high standard demanded by the service and Londoners themselves. You cannot avoid that duty. Nor can I.
"I will not stand for any racism or racists in the Met."
Pc Alex MacFarlane of the Metropolitan Police has been suspended after a recording was made of a suspect being called a "n*****".
The arrested man, named as Mauro Demetrio, 21, from Beckton, east London, was arrested on suspicion of drug driving but no action was later taken.
He recorded the abuse on his mobile phone.
It later emerged that another officer, reportedly with Pc MacFarlane when Mr Demetrio was abused, was placed on restricted duties after later being allegedly seen kicking a 15-year-old black boy to the ground and kneeing him.
The incident was said to have happened in the custody area of an east London police station with part of the incident recorded on CCTV.
