Belsize could refer to:
* Belsize Park – also known as 'Belsize' – a neighbourhood in London, the United Kingdom
* Belsize (ward), a ward named after Belsize Park, London
* Belsize Lane, a street in Belsize Park
* Belsize Park Gardens, a street in Belsize Park
* Belsize House, historic house
* Belsize Road, a street in South Hampstead, London
* Belsize, Hertfordshire, a hamlet in Hertfordshire
* Belsize architects, a firm of architects based in Belsize Park, London
* Belsize Motors, a former automobile-manufacturing firm based in Manchester
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