The chain came under fire from Labour MP Paula Sherriff, who sits on the House of Commons select committee, following reports by the BBC this summer that WHSmith were charging higher prices for products such as stationary and water across its 128 hospital stores.
Sheriff said the practice was "fundamentally wrong" and that patients and visitors were "effectively being exploited".
Following a meeting with the Dewsbury MP, WH Smith agreed it will match stationary prices going forward and make sure that average selling prices across all ranges "remain aligned.”
The company denied that it ever charged £1.89 for a 750ml bottle of Buxton water, saying that at the time of the reports in August, the water cost £1.49 in hospital stores compared to £1.00 on the high street but that was part of a special till promotion.
A spokesperson said: "“The vast majority of our products are the same price in both our hospital and high street stores. This includes all newspapers, magazines, books and stationery. For food and drinks, where prices may be different, they are very similar and often slightly cheaper in Hospitals reflecting the different sales mix and the resulting promotional approach which is designed to best deliver value to all of our customers, despite the different cost structures.
Sheriff said: "This is a welcome first step for NHS patients, visitors and staff, who were frankly being exploited to boost the bottom line of some of Britain's biggest businesses while the government looks the other way. It's appalling that ministers have refused to act, but I will be meeting other retailers soon and I hope they will follow this lead.
"Whether it's higher prices in the shops or charging for car parks, those who use or work in our hospitals are the paying an unfair price and it's about time to change it."