A swastika and antisemitic slogans were scratched on the wall of a kosher cafe in Hendon Park on Monday night.
Hendon Park Cafe owner Jason Ezekiel was informed of the graffiti by a park keeper. "He had already painted over some of it as he didn't want to upset Jewish people. I am very distraught by the whole thing."
Mr Ezekiel believed the perpetrator used a key. "It must have taken at least 20 minutes to do."
Community Security Trust communications director Mark Gardner said: "This was a particularly ugly incident in a peaceful location that is popular with many families."
A Barnet Council spokesman pointed out that it maintained a zero tolerance approach to racism and had "removed the offending graffiti immediately".
Police are investigating the incident and have urged witnesses to ring 0300 123 1212 or Crimestoppers anonymously on 0800 555111.
The cafe opened in May.