This study was carried out to investigate a horizontal mowing knife machine (HMKM) for mowing alfalfa in small fielding's and consequently reducing mowing costs. Speed ratio of 0.86, 0.94 and 0.98; working width of 0.6, 0.8 and 1.0 m and mower knife height of 4, 6 and 8 cmwere studied. Mower efficiency, field capacity, fuel consumption, consumed energy and economic costs were computed. The main results showed that increasing speed ratio and working width result in increasing mower efficiency, field capacity, fuel consumption, economic cost but consumed energy decreased. Increasing mower knife height leads to increase mower efficiency while decreasing fuel consumption, consumed energy and economic cost. The maximum values of mower efficiency was 96.9%, field capacity of 0.66 fed/h, fuel consumption of 2.3 lit/h, machine consumed energy of 17.768 kW.h/fed, and the economic cost decreased by 54.7% at speed ratio of 0.86, working width of 0.6 m and mower knife height of 4 cm comparing to manually sickling conditions.