The Restaurant Group, the owner of the Frankie & Benny's and Chiquito chains, will sell or close 33 outlets.
Restaurant Group, which runs 500 theme restaurants, said it had been a "challenging trading period".
It said its Frankie & Benny's chain had "suffered due to insufficient focus on value, unsuccessful menu development and poor operational execution".
Those outlets had lost customers after "significant price increases and the removal of popular value offers".
The company said it was "taking action" to change this, adding it would stick with the Frankie & Benny's brand as it remained "relevant and popular".
The group said the introduction of "more 'authentic' menus without sufficient testing of the concept", and the removal of many popular dishes from menus had failed to please.
The dishes also took longer to prepare.
A spokesman for the group said that customers cited price as their main concern about the new menu, which was introduced across the 250-strong chain in 2015.
Around half of the restaurant closures planned would be across the Frankie and Benny's chain, leaving it with around 235 outlets.
The restaurant critic and broadcaster, Jay Rayner, told the BBC that mid-market restaurant chains, like those owned by The Restaurant Group, were potentially among the sector's most lucrative.
As a consequence, consumer choice had proliferated, leaving competition for premises and personnel intense.
The firm said it would take a £59.1m charge linked to the site closures, pushing it into a half-year loss of £22.5m.
Across Restaurant Group as a whole, total revenue rose 3.4% to £358.7m in the first half of the year, but like-for-like sales dropped 3.9%.
Earlier this month, the company made key management changes, including removing chief executive Danny Breithaupt, and replacing him with the former boss of Paddy Power, Andy McCue.