Phenotypic diversity of 482 landraces and improved cultivars in foxtail millet mainly originating from Henan, Hebei, and Shandong provinces, China was investigated based on a field evaluation of 11 morphological and agronomic traits. Compared to the landrace cultivars, the improved cultivars had smaller diversity index and narrower frequency distribution of different types in the traits investigated. The mean plant height of the improved cultivars was significantly lower than the landraces. The improved cultivars had greater spike weight, grain weight per spike, and percentage of grain weight per spike in comparison with the landraces. The broad genetic diversity of the landraces is a valuable genetic resource for developing foxtail millet cultivars.