Production and sale of livestock in Kenya has been changing in terms of quantity over time. As population, urbanization and income growth increases, pastoral livestock keepers should be able to respond to potential increases in demand for livestock and livestock products by releasing small ruminants into the market. This study critically examines the sales decisions of the rural livestock keepers in the arid and semi arid lands (ASALS) of Kenya by analyzing the significant determinants of the market participation decisions in small ruminants market by the pastoral livestock keepers. The study was carried out in Isiolo and Marsabit Districts where data were drawn by interviewing a sample of 250 livestock keepers through administration of structured questionnaires in July 2010. These were supplemented with secondary data from libraries and government offices in the study area. The two step selectivity model was used to analyze the data collected from the study. The study results show that road conditions to the markets, price for small ruminants, group membership, cash relief, credit facilities and the herd size are the significant determinants of market participation decisions by livestock keepers. The study recommends that in order to increase participation of livestock keepers in the small ruminant market, it is imperative to improve the conditions the of the roads, discourage reliance of pastoralists in relief by promoting diversification of activities in the ASALS and motivate pastoralists to be commercially oriented by focusing on investments that result in marketable surplus through increased production.