Marine Le Pen was egged by protesters while out on the campaign trail in Brittany.
Footage emerged showing Le Pen, who is standing for the far-right Front National in the French presidential election, being hit on the back of the head by an egg.
She was out and about in Dol-de-Bretagne, meeting French voters, and was surrounded by the media when the egg was thrown.
The protesters accused her and her party of being fascists. Her bodyguard quickly ushered her away as she ducked her head.
The moment was caught on camera by the French broadcaster LCI.
Polls suggest Le Pen is on course to lose the election at the end of May as the French public vote in the second round of the election.
Her rival is the centrist candidate Emmanuel Macron, whose party, En Marche!, was formed around a year ago.
French pollsters have Marcon on around 59% and Le Pen 41%. However, around a fifth of French voters are still undecided.
The pair clashed in a television debate on 3 May watched by as many as 20 million people.