Nick Clegg was hit by a blue paint bomb by two disgruntled activists during a Liberal Democrat event in Glasgow on Thursday evening.
The paint hit the deputy prime minister in the face and on the back of his jacket.
One man has been arrested for breach of the peace after the attack. No details have been released but Scottish news outlet STV reported he was in his 20s and protesting against the party's decision to go into coalition with the Conservatives in Westminster.
Clegg shrugged off the event, telling Real Radio Scotland: "These things happen. It's not a big deal."
Leader of the Scottish Liberal Democrats Willie Rennie, who was attacked with Clegg said: "It was two disgruntled individuals, who chose not to speak about their concerns in advance but were purely interested in a stunt. Their behaviour has only obscured any message that they may have had."
He joked: "I've always wanted a blue streak in my hair but my mother wouldn't let me."
Nick Clegg's spokesman said he would not "allow a bit of paint to stop him speaking to Liberal Democrats in Glasgow - that would be ridiculous", the BBC reported.
Labour MP for Glasgow South Tom Harris condemned the attack, tweeting: "I'm not exactly Clegg's biggest fan but this kind of attack is shameful and quite pathetic."