Abstract: Eocrinoids are very abundant in the Middle Cambrian Kaili Biota at Balang village, Jianhe County, Guizhou Province. Two species are present: the long stalked Sinoeocrinus lui Zhao, Huang et Gong, 1994 and the short stalked Sinoeocrinus globus Zhao et al., 1999. Over 10000 well preserved specimens have been collected including complete ontogenetic series for the two species. These specimens all show brachioles, thecae, stalks and attached discs, and a few specimens show anal pyramids. The development of surtural pores on the thecae appears as an obvious change during different growth stages. The surtural pores are not developed in juvenile stages, but are welldeveloped in adult individuals of both species. Most eocrinoids exhibit a solitary lifestyle. The theca of short stalked eocrinoids is spheroidal, with a large attached disc, often found attached to fragments of brachiopod shell, or to cranidia, or to thoracic segments of trilobites. The long stalked form possesses a small attached disc, which is often attached directly to the silty mudstone substrate. The brachioles of both species are also distinguished by two different growth modes, in which the long stalked forms grew straight up and the shortstalked forms grew spiral up. These characteristics are important in understanding the diversity, ontogeny and ecology of eocrinoids assemblages from the Kaili biota.