Ust’-Polui is one of the most extensively studied archaeological sites in the western Siberian Arctic. New radiocarbon (14C) dates for charcoal, faunal remains, bark, hide, and human bone from this site are presented. When modeled, the charcoal dates span from ~260 BC to 140 AD, overlapping with the dendrochronology dates from the site. These dates also overlap with the expected age of the site based on artefact typology. 14C dates on reindeer bone have a slightly younger modeled age range, from ~110 BC to 350 AD. In contrast, dates on the site’s numerous dog remains, and on human and fish bone, all predate these modeled age ranges by over 500 years, despite being from the same deposits. Several sets of paired dates demonstrate significant age differences. Bone dates with lower δ13C values tend to be over 500 years older than those with higher δ13C values. Stable isotope data for the humans, dogs, and other faunal remains are also presented. These data suggest the dogs and the humans were regularly consuming freshwater fish. The dogs were probably fed fish by their human counterparts. Overall, the dog and human dietary patterns at Ust’-Polui created 14C dates biased with major freshwater reservoir effects.