Tredegar Town Band was the winner in the second session on Saturday 3 May.
Coming top means they are now in contention for the competition's final grand prize of £10,000.
Following the broadcast of all four sessions, the winners in each will then be considered for the top prize in the series finale on 24 May.
"We're delighted. The band played great today," said Ian Porthouse, the band's Musical Director as they were named the winners.
Tredegar Town Band have gained much success in national and international competitions and is currently ranked second in the World Brass Band Rankings. But competing against wind and jazz bands in Band Cymru was a new experience for them.
"This was a different type of competition for us, and I am very proud of everyone," adds Ian Porthouse.