Wetlands including lakes and swamps sediments are natural archives that provide long-term records of past changes in climate-catchment processes as well as changes in biological communities. Diatomaceous sediment deposits are natural archives of palaeoclimate and their analyses have provided a wealth of interesting and important information about palaeoenvironmental investigations and climate change (Owen, 2002; Owen and Renaut, 2000; Barker et al., 1990; Feibel et al., 1991). A lot of palaeoclimatic data (in Kenya and Eastern Africa) have been gathered from large lakes (Lake Victoria, Lake Turkana, Lake Naivasha, Lake Malawi, Lake Tanganyika), small lakes primarily in the Rift Valley system, and from maars and tarns at high altitude sites such as Mount Kenya. This paper aims to study the palaeoclimate of the last

1.000 years for the Nairobi area on the western flank of the Kenya Rift Valley, based on analysis of the lithology, diatom assemblages and sediment geochemistry of Ondiri Swamp. Ondiri Swamp is located at latitude 36°40′ and longitude 1°15′ in Kikuyu Division of Kiambu District approximately 10 km west of Central Nairobi in Central Province, Kenya (Figure 1). The swamp is a major source of Nairobi River that drains to the Athi River which eventually empties into the Indian Ocean.