In Tanzania, farmers like others elsewhere, have to make informed choices of optimum and cost effective farm machinery. The level, appropriate choice and subsequent proper use of farm machinery has a direct and significant effect on productivity. Tanzanian farmers use traditional intuitive farm machinery selection methods which, in most cases, results in uneconomical investment. The overall objective of this study was to develop a computer-based decision support system tool for selecting optimum tractor-plough systems in Mvomero District. This objective was achieved by initial assessment of the status of agricultural mechanization in the study area. Soil and terrain physical properties including soil bulk density, texture, moisture content, cone index, and slope gradients were determined to form a baseline data for selecting suitable farm machinery. Under the determined soil and terrain characteristics, tractor-plough system’s field performance parameters were subsequently determined. Theoretical mathematical models were developed for the simulation of tractor-plough system’s static overturning stability limit on slopes. Using SPSS software, regression models were developed to predict the tractor- plough system’s field performance and static overturning stability. Employing mathematical models developed in this study and from the literature, a computer-based Tractor-Plough System Selection Tool (TPSST) was developed. The TPSST used procedures and functions from the database to process data entered by users and displayed the least-cost set of tractor–plough system along with other alternative sets. A sample of TPSST output identified a least-cost set of two tractor-plough systems which are capable of completing a 100 ha farm within allotted time. The set comprised of a 74kW tractor/1.25 m plough system and a 31 kW tractor/0.99 m plough system. The simulation output for the 74 kW tractor-plough systems included: 32 kN0 drawbar pull, 26 kN draught force, 16.5l/h fuel consumption and TZS 3 665 720 total annual cost. Theiii simulation output for the 31 kW tractor-plough systems was: 12 kN drawbar pull 4 kN, draught force, 6.9 L/h fuel consumption and TZS 1 665 193 total annual cost. It is expected that the TPSST will assist in performing tasks of different agricultural mechanization stakeholders including designers, manufacturers, researchers, trainers, farm machinery managers, extension staff and consultants.