1) Fire has shaped biological responses of plants and plant communities in fire-prone systems and is linked to myriad ecological processes but also frequently puts people and infrastructure at risk. Fuel or hazard-reduction burning is a common practice aimed at reducing the risk of high-severity fires, which ideally also incorporates consideration of biodiversity values. Within fire-prone systems, seed banks are often critical for plant species’ regeneration, and seeds are typically adapted to survive the passage of fire and to regenerate in response to cues associated with natural fire regimes. However, species-specific tolerances to the heat from fire exist; likely influenced by a range of physical, physiological, and morphological seed traits. Identification of these tolerances and associated seed traits may inform fire and species-management. 2) We determined the lethal temperatures for seeds in relation to their moisture content, and other key traits that we hypothesised may be associated with survival. Seeds from 14 native species, and 4 species invasive to fire-prone Mediterranean climate Banksia woodlands of southwestern Australia, were exposed to temperatures between 50 °C and 180 °C for 3 mins, at three different moisture contents. The temperature at which half the seeds were killed (T50) was estimated using non-linear log-logistic modelling. Seed mass, seed shape, embryo type, plant resprouting ability, seed storage syndrome, and native/invasive status, were measured and modelled for their correlation with T50. 3) Increased moisture content was a significant predictor of elevated seed mortality. Seeds with low moisture content (those pre-conditioned at 15 or 50% RH), were able to survive far hotter temperatures (median increase of 38 °C and 31°C respectively), than those with high moisture content (those pre-conditioned at 95% RH). Of other traits considered, seeds with basal embryos showed significantly lower T50 than other embryo types. 4) Synthesis: Seeds with higher moisture contents have lower lethal temperature thresholds, leading to higher seed mortality during fire events when seeds (and soils) are moist. Thermal tolerance varied among co-existing species within this fire-prone system. These data suggest potential concern for the impacts of aseasonal burning practices (i.e. cool/wet season burning), and highlight the importance of taking seed moisture content into account when planning and implementing prescribed burning.