The blonde beauty was dressed for the summer weather as she opted for a bright pink dress with a navy hem and pretty floral pattern.
She teased viewers with a glimpse of her cleavage in the plunging outfit as she resumed her duties at the numbers and letters board.
Her décolletage was left exposed due to the low-cut style of her halter-neck dress, which clung to her body, highlighting her svelte figure.
The bright number cinched in at the waist before flaring out into a skater skirt that grazed her knees.
Countdown's Rachel Riley thrilled as she flashes cleavage in plunging dress
Her décolletage was left exposed due to the low-cut style of her halter-neck dress
Rachel, 31, teamed the stunning frock with a pair of matching heels, which featured a navy pointed toe.
Her golden tresses were styled in cascading curls while she appeared to be sporting lashings of mascara and a slick of pink lipstick to complement her attire.
Earlier today, the former Strictly Come Dancing star took to Twitter to express her outrage that Arsenal owner Stan Kroenke was launching a TV channel dedicated to showing animals being hunted.
The bright number cinched in at the waist before flaring out into a skater skirt
Rachel Riley in pictures
Fri, March 3, 2017
Rachel Riley is the Carol Vorderman of the naughties. She co-hosts Countdown and here are some of her best pictures
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Rachel Riley steals the show in baby blue dress
Rachel's golden tresses were styled in cascading curls
She shared an article regarding the news on her official Twitter page before commenting on the piece herself.
Rachel simply wrote "disgusting" next to the article, with several of her 496,000 followers agreeing.
Countdown airs weekdays on Channel 4 at 2.10pm.