The Grub Street Opera is a play by Henry Fielding that originated as an expanded version of his play The Welsh Opera. It was never put on for an audience and is Fielding's single print-only play. As in The Welsh Opera, the author of the play is identified as Scriblerus Secundus. Secundus also appears in the play and speaks of his role in composing the plays. In The Grub Street Opera the main storyline involves two men and their rival pursuit of women.
The play is Fielding's first truly political play and first ballad opera. Unlike The Welsh Opera, the play deals with morality from the beginning. Additionally, it linked to Fielding's previous attacks on the London theatre and inept writers. Fielding also used the virtue of female servants as a point of humour and to discuss morality, while using the effeminacy and dominance by women to mock various characters and discuss the issue of gender roles. Critics viewed The Grub Street Opera positively, noting it to be a definite improvement on The Welsh Opera.