AF Blakemore's retail arm will spend £250,000 converting the sites in Wales, which became available when the Office of Fair Trading told The Co-op to sell 110 stores following its purchase of Somerfield.
The 5,200 sq ft Builth Wells store will become the larger-format Eurospar, while a 3,000 sq ft store in Buckley will become a Spar.
"We think the stores will do very well for us," said Tates MD Geoff Hallam. "We are making a big investment converting the stores and bringing them up to a high standard."
Tates won The Grocer's Gold Independent Retail Chain award and last year opened its first UK Eurospars, in Sheffield and Nottingham. It is seventh in The Grocer's Top 50 Independents this week.