The £300 million deal makes HCOne, formed after the collapse of Southern Cross in 2011, the UK’s biggest care-homes owner.
Bupa will retain about 150 care homes and six Richmond Villages.
It said it would invest more than £120million on refurbishing existing facilities and building new homes and villages.
HC-One chairman Dr Chai Patel said: “Today’s news represents a true highlight of my 30-year career, which started as a junior doctor on NHS wards in Southampton.
“The acquisition is the latest step in the expansion of our provision of the very best and kindest care.
“The homes we have acquired from Bupa are dispersed across the UK, and demonstrate HC-One’s ongoing strategy.”