Using the minirhizotron technique, we investigated the vertical distribution and seasonal dynamics of fine roots of Populus euphratica, the dominant tree species of the riparian forests in the extremely drought area in Ejina, Inner Mongolia. The results showed that: 1) In general, the maximum of root length density and root surface area density appeared in the 0-20cm soil layer (P<0.05). 2) The average growth rate and the ratio of growth rate to death rate in the top soil layer (0-40 cm) were both higher than those in the deep soil layer (40-80cm) in the growing season. 3) As a whole, the root length density, root surface area density and growth rate showed a similar seasonal tendency with the peak value occurring in the middle period of growing season, but the death rate increased gradually. Meanwhile, the ratio of growth rate to death rate decreased gradually from April to September and dropped to < 1 at the end of the growing season. 4) The seasonal changes of growth rate and death rate were significantly and positively correlated with soil temperature (P<0.01), and there was a significant correlation between growth rate and soil water content (P<0.01). However, no significant correlation could be detected between seasonal change of death rate and soil water content (P>0.05).