A filling factory was a manufacturing plant that specialised in filling various munitions, such as bombs, shells, cartridges, pyrotechnics, and screening smokes. In the United Kingdom, during both world wars of the 20th century, the majority of the employees were women.

In World War I, a filling factory belonging to the Ministry of Munitions was known as a National Filling Factory.

In World War II, a filling factory belonging to the Ministry of Supply was known as a Royal Filling Factory (RFF), or a Royal Ordnance Factory (ROF). These were all part of the Royal Ordnance Factory organisation, owned by the MoS.

The filling of smoke screen canisters and other pyrotechnic devices was also carried out by fireworks manufacturers, particularly in World War II, but these are not specifically covered by this article.