Professor Popper's Problem is a 1975 British children's science fiction comedy film directed by Gerry O'Hara, starring Charlie Drake in the title role. Featuring a number of child actors, Todd Carty, Milo O'Shea, and Sydney Bromley also appear. The serial picture was produced for the Children's Film Foundation (CFF) by Roy Simpson of Mersey Film Productions, presenting a screenplay by Leo Maguire and soundtrack by Kenneth V. Jones. The story concerns an eccentric science teacher named Professor P. Popper, miniaturised with a group of pupils after accidentally consuming shrinking pills. A student apart from the group volunteers her help, as, separately, does a colleague of Popper's. As they search for an antidote, Popper and his entourage must see off multiple dangers, including criminals determined to steal his shrinking formula.

Filmed at Elstree Studios in Hertfordshire, Professor Popper's Problem was serialised into six 14 to 16 minute episodes for television viewing. Akin to other CFF features of the 1970s, the film broke with the Foundation's earlier releases by accurately representing aspects of working-class Britain, albeit through a science fiction narrative. Though restricted by a small budget, props and special effects defined the film; in this respect, O'Hara praised Tom Howard for his work on the picture. Reviews have been few and mixed from its release on 1 January 1975. Upon immediate showings, the film was characterised as unpretentious entertainment. Conversely, the picture has since been appraised as a low-point in Drake's career, simply by his agreeing to act in something perceived as so small. These criticisms have nevertheless been matched by retrospective assessments approving of the film's realistic depictions of 1970s Britain, in addition to Drake's subsequent theatrical roles.