I Brigade, Royal Horse Artillery was a brigade of the Royal Horse Artillery which existed in the early part of the 20th century. It was dissolved at the outbreak of World War I as its constituent batteries were posted to other formations. Post-war, the brigade was reformed, serving in the UK, Egypt and India before being redesignated as 1st Regiment, RHA in May 1938 at Aldershot. The brigade had an earlier incarnation as A Brigade, RHA, formed from the Horse Brigade, Royal Artillery in 1864 before being broken up in 1889.