St. John's Gardens (Welsh: Gerddi Sant Ioan) are a small public garden in the center of the Welsh capital Cardiff in United Kingdom. It is located between St John's Church and the Old Library. The park is around 1000 m² in size and is enclosed by cast iron railings. The gardens have some old trees (including a large magnolia tree), some flower beds, a central hut and several benches. The railings and gates (dating from the 1890s) are Grade II listed. The wooden hut at the centre of the gardens is also Grade II listed.