The 20th Mounted Brigade previously known as the 2/1st Lowland Mounted Brigade was a second line yeomanry brigade of the British Army during the First World War. Raised after the declaration of war, it was a mirror formation of the first line Lowland Mounted Brigade. It had under command the 2/1st Ayrshire (Earl of Carrick's Own) Yeomanry, the 2/1st Lanarkshire Yeomanry, and the 2/1st Lothian and Border Horse. All of which were converted in cyclist units in 1916, the brigade, never having seen any active service, ceased to exist.