The Democratic Party of Japan, the nation's biggest opposition party, will merge with Ishin no To (Japan Innovation Party) in a bold institutional shake-up aimed at preparing for the key Upper House election in summer.

The move will hopefully spruce up the DPJ's battered public image, party officials said Tuesday.

The merger, which is slated to take place by the end of March, will create a party with 93 members in the 475-seat Lower House and 59 members of the 242-seat Upper House.