U.S.-listed shares of Unilever rose 10.1% on the news, while GSK's fell 2.8%. The two stocks also trade on the FTSE, where the day's trading had closed.
GSK has rejected three bids from Unilever for its consumer arm, which is home to brands such as Sensodyne toothpaste, Emergen-C vitamin supplement and Panadol painkiller, saying the bids "fundamentally undervalued" the business and its prospects.
It has said it would stick to its plan to separately list the business in mid-2022 and issued improved financial assumptions for the unit.
Unilever said in a statement it had noted these but "determined that it does not change our view on fundamental value. Accordingly, we will not increase our offer above £50 bln".
A spokesperson for GSK responded that the group was strongly focused on maximising shareholder value and very confident in the future of the consumer healthcare business in which Pfizer has a 32% stake.
"The Consumer Healthcare business has an exceptional portfolio and offers existing and prospective shareholders a highly attractive financial profile supporting investment and future returns," they added.
In a statement rebuffing Unilever's overtures last weekend, GSK said the bid failed to capture the unit's potential, releasing new forecasts that projected annual organic sales growth of 4%-6% for the business, which made sales of 9.6 billion pounds last year, over the medium term.
This estimate was above its prior forecast of seeking to beat the consumer health market's growth of about 4%.
The British drug maker said it intends to further share details of its strategy for the consumer brands unit at an investor day on 28 February.
The event would follow its fourth-quarter results on 9 February where it might also throw some light on its thinking.
Unilever's decision not to raise its bid comes after analysts and investors widely panned its offer, sending shares in the maker of Dove soap down 8% on Monday, on worries about the financial implications for the company.
A source familiar with Pfizer's strategy told Reuters earlier this week that GSK and Pfizer would open negotiations with Unilever's boss Alan Jope if the consumer goods giant was ready to improve its bid to more than 60 billion pounds.
(Corrects JAN 19 story to make clear Pfizer has stake in consumer healthcare business, paragraph 6)
($1 = 0.7337 pounds)
(Reporting by Siddharth Cavale, Aby Jose Koilparambil in Bengaluru and Ludwig Burger in Frankfurt; Editing by Devika Syamnath, Alexandra Hudson)