France's TF1 is seeking £78m in compensation and Telecinco, the Spanish broadcaster also owned by Berlusconi, are also suing.
Broadcasters are becoming increasingly intolerant of Google using their content without agreeing proper terms, such as those signed by rivals MySpace, Veoh and Dailymotion.
Mediaset kicked off its legal bid yesterday when it filed a writ at a civil court in Rome against YouTube and Google for unlawful dissemination and commercial exploitation of audio-video files owned by the Mediaset.
Mediaset said that its lawsuit follows an audit it carried out on June 10 on YouTube, which found at least 4,643 video files that it owns. It said this amounted to over 325 hours of material that was being aired on YouTube without rights. It said this was the equivalent of 315,672 days of broadcasting lost by its three TV channels.
Mediaset said its claim included at least £395m in losses incurred for non-sale of advertising space on the programmes unlawfully shown on YouTube.
In a statement, Google said: "There is no need for legal action. We prohibit users from uploading infringing material and we cooperate with all copyright holders to identify and promptly remove infringing content as soon as we are officially notified."