Olorgesailie is noted for the large number of Acheulean hand axes discovered there that are associated with animal butchering. According to the National Museums of Kenya, the finds are internationally significant for archaeology, palaeontology, and geology.

Human tools are the most prominent of all historic items in the area. The abundant hand axes are characteristic of the Acheulean period, made by hominins between about 600,000 and 900,000 years ago along what was then the shore of a now dried-up lake. Fossils of various animals have also been found, including those of extinct species of hippo, elephant, zebra, giraffe, and baboon, likely to have been butchered with the aid of the hand axes.

In June 2003, a team led by Potts discovered a frontal bone in situ. Other parts of the small skull (designated KNM-OL 45500) were found in the following months. The frontal bone is 900,000 to 970,000 years old and probably belonged to Homo erectus, thereby making it the first human fossil found on the site. The fossil remains were in the same stratigraphic level as two hand axes and several flakes, near dense deposits of hand axes.

In 2018, evidence dating to about 320,000 years ago was found at Olorgesailie of the early emergence of complex and modern behaviors, possibly associated with early Homo sapiens, including the trade and long-distance transportation of resources (such as obsidian), the use of pigments, and the possible making of projectile points. The emergence of these behaviors, it is observed by the authors of three 2018 studies on the site, approximately corresponds to the earliest known Homo sapiens fossil remains from Africa (such as at Jebel Irhoud, Morocco, and Florisbad, South Africa) dated to about the same period, and it is suggested that complex behaviors began in Africa around the time of the emergence of Homo sapiens.