UFC on Fox: Shevchenko vs. Peña (also known as UFC on Fox 23) was a mixed martial arts event promoted by the Ultimate Fighting Championship held on January 28, 2017, at Pepsi Center in Denver, Colorado.

A potential UFC Women's Bantamweight Championship title eliminator between multiple-time muay thai world champion Valentina Shevchenko and The Ultimate Fighter: Team Rousey vs. Team Tate bantamweight winner Julianna Peña served as the event headliner.

A bantamweight bout between Raphael Assunção and Aljamain Sterling was originally booked for UFC Fight Night: Lewis vs. Abdurakhimov. However, Sterling pulled out due to an undisclosed injury. The fight was later rescheduled for this event.

Yancy Medeiros was expected to face Li Jingliang at the event. However in early January, Medeiros pulled out for undisclosed reasons and was replaced by promotional newcomer Bobby Nash.

A middleweight bout between former Bellator Middleweight Champion Hector Lombard and Brad Tavares was expected to take place at this event, but was scrapped on January 10 due to undisclosed reasons.

A week before the event, promotional newcomer John Phillips pulled out of his light heavyweight bout against Marcos Rogério de Lima and was replaced by fellow newcomer Jeremy Kimball.

At the weigh-ins, de Lima came in at 209.5 lbs, over the light heavyweight limit of 206 lbs. As a result, de Lima was fined 20% of his purse, which went to Kimball and the bout proceeded as scheduled at catchweight.

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