Protesters greeted President Jacob Zuma as he arrived at South Africa House today as part of his state visit to the UK.
With the chant of "Shame on You, Zuma" ringing out, the South African leader was met at the High Commission in London by around 50 demonstrators.
They are angered by what they see as his failure to pressure Zimbabwe's Robert Mugabe into reform.
Earlier this week the South African president called for international sanctions on Mr Mugabe and his inner circle to be lifted.
Campaigners accuse President Zuma of appeasing Mr Mugabe.
They believe he should be doing more to ensure fresh elections are called in Zimbabwe.
Demonstrators held aloft banners proclaiming "Zuma Save Zimbabwe" at today's protest while a man in a Mugabe mask wandered around with a sign stating "Zuma - have another wife on me".
Rose Benton, co-ordinator of the Zimbabwe Vigil - a weekly demonstration outside the Zimbabwean embassy - said: "The government of national unity isn't going to work, Mugabe isn't serious about making it work - he never has been.
"What we need is Zuma to do something."
As he walked up a red carpet to the High Commission entrance, the South African leader turned and waved at the protesters.