The shift from pastoral to agro-pastoral farming system is on-going among the Maasai community in Trans-Mara West district of Kenya. This community has had a long time history in pastoral livelihoods, but are increasingly engaged in the shift, in spite of the Kenyan Government effort to set up co-operative societies for marketing livestock and livestock related products. Essentially, these co-operatives are supposed to trigger extensive expansion in livestock production which in turn could have implication on natural resource conservation. Despite this effort, pastoralists in the area are not sufficiently responsive as evidenced by the ongoing gradual shift. The push and pull factors between the pastoral and agro-pastoral livelihoods necessitates clarity. The shift in livelihoods could be following a rational and economic decision with impacts on the diversity of livestock and crops but empirical evidence is lacking to ascertain this assumption. Evaluating household decision making associated with the shift, may explain the rationale of observed behavior and inform development strategies for such areas. Specific objectives of the study were to compare differences between pastoral and agro-pastoral based livelihoods for: - socio-economic characteristics of practicing households, diversity in crops and livestock enterprises, economic benefits of the farming systems and to determine the factors associated with the shift. Stratified proportionate random sampling procedure was used to get the appropriate sample. Data were collected from a sample of 130 households through interview schedule. Data was subjected to chi square and t-test statistics while diversity of crops and livestock was based on Shannon index. An economic evaluation model was used to compare economic benefits while Heckman two-step model was used to determine the factors associated with the shift to agro-pastoral farming. The findings indicated that agro-pastoral households were older farmers with declining farm size, stronger in social capital and more inclined to diversification of livelihoods. They had better access to credit facilities and extension services. Shannon index of diversity for crops was 0.3 units higher in agro-pastoral farming where unit net economic benefits were 0.02 times greater. The shift from pastoral to agro-pastoral livelihoods was enhanced by more frequent group meetings and farmer trainings, declining land sizes, longer distance to watering points, shorter distance to market and more income from off-farm sources of incomes. The agro-pastorals choice to allocate higher proportion of land for crop production compared to livestock production was enhanced by more distance to watering points, low off-farm incomes, private land ownership, larger family, male dominance, more extension services, shorter distance to the market, less years of crop farming and little interaction with the neighbors.