Abstract: This paper deals with the floristic characteristics of Typhaceae etc. four families in southwestern Hubei, based on the specimens collected during the exploration to this area in 1985 and a lot of data surveyed. The results show:1. The flora so far known comprises 5 genera, 20 spp., 2 vars. and 1 hybrid, among which Sparganium fallax Graebn., Potamogeton perfoliatus L. and P. obtusifolius Mert. & Koch. are new records to Hubei, P. intortusifolius J. B. He et al. and Najas graminea Del. var. recurvata J. B. He et al. are new species and variety, respectively. 2. This area abounds in the species of these four families, as compared with the other provinces or districts of China, only next to Heilongjiang, Jilin, Yunnan, Xinjiang, Shaanxi, Intramongolia and the rest part of Hubei. Of 24 taxa of these four families found in the rest part of Hubei, 19 have been collected in this area. Thus the flora studied undoubtedly represents that of Hubei.3. The flora is of old origion, for the family Sparganiaceae being a Mesozoic one and the rest three at least Tertiary ones.4. The floristic element endemic to southwestern Hubei contributes a certain propotion (c. 8.70%) to the floristic composition.5. The floristic components are complex, 12 types of distribution area being divided. But its composition is mainly of cosmopolitan (26.09%) and temperate E. Asian (including Sino-Japanes) elements (26.09%).6. The flora is chiefly very close to that in the provinces or districts on the Tertiary terrace of the geomorphological map of China, namely east of China, which implies that there is an unanimity in the floristic regionalization at the level of the subregions between these four families and terrestrial seed plants.