We initiate a series of publications on the flora of the province of Soria, Spain, which are previous to the review and reedition of the Floristic Catalogue of Soria (SEGURA & al., 2000), to incorporate 50 taxa corresponding to vascular plants which had not previously been recorded for the flora of province of Soria. Since the level of prospection in the Province is currently very high, these recent findings are all rare and scarce taxa in the province?s territorial context; some are peripheral or much localized, others are restricted to scarce environments and require them to be well preserved; in general, they show a presence extent very diffuse or fragmented in the Province. Another part are taxa recently described, commonly of a sub specific rank. All of them provide with an enlargement of their known distribution area, or with an improvement in their demarcation. Some floristic rarities and some regional novelties stand out, such as Beta maritima, Hippocrepis bourgaei or Lappula patula, besides other species that are very scarce, peripheral, relict or showing a fragmented area of distribution in the Province, such as Arbutus unedo, Hieracium prenanthoides, Gagea foliosa subsp. durieui or Hyacinthoides non-scripta.