Mongolian steppes are still under traditional land use by mobile pastoralism and remain relatively intact. Traditional ecological knowledge (TEK) has always played an essential role in herders' assessments of pasture conditions, and decision-making regarding their movements. In the last two decades, Mongolia's rapid socio-economic development resulted in dramatically increasing livestock numbers and expanding settlements, raising concerns about rangeland degradation associated with potential declines in herders' TEK. We compared quantitative and qualitative data from interviews on herders' TEK and standard ecological assessments to assess the level of congruence. In 2020, a total of 367 households across ten sampling sites were interviewed about pasture condition, TEK on forage and degradation indicator plants. For the same sites, we collected field-based data on plant species richness, composition and biomass, as well as remote sensing-derived biomass estimates. Our results highlight variance in TEK: even within the same sites, there were widely diverging perspectives on pasture condition and its trends, forage palatability and degradation indicator plants, suggesting that there is limited exchange among herders. Multivariate analyses showed that herders' assessments had a moderate association with field-based vegetation data, reinforcing that comprehensive evaluations of pasture conditions still require field-based assessments. These findings underscore the need for stronger communication between scientists and herders, as well as enhanced transfer of TEK regarding current and changing pasture conditions. Since TEK and its transmission play a key role in herders' movement decisions and are vital for future rangeland monitoring, capacity building is recommended to support the development of sustainable land use policies that uphold ecological integrity.