Power tiller is a major unit of agricultural machinery being used on farms in Korea. About 180.000 units are introduced by 1977 and the demand for power tiller is continuously increasing as the farm mechanization progress. Major farming operations done by power tiller are the tillage, pumping, spraying, threshing, and hauling by exchanging the corresponding implements. In addition to their use on a relatively mild slope ground at present, it is also expected that many of power tillers could be operated on much inclined land to be developed by upland enlargement programmed. Therefore, research should be undertaken to solve many problems related to an effective untilization of power tillers on slope ground. The major objective of this study was to find out the travelling and tractive characteristics of power tillers being operated on general slope ground.In order to find out the critical travelling velocity and stability limit of slope ground for the side sliding and the dynamic side overturn of the tiller and tiller-trailer system, the mathematical model was developed based on a simplified physical model. The results analyzed through the model may be summarized as follows; (1) In case of no collision with an obstacle on ground, the equation of the dynamic side overturn developed was: $$sum_n^{i=1}W_ia_s(cosalpha cosphi-{frac {C_1V^2sinphi}{gRcoseta})-I_{AB}frac {v^2}{Rr}}=0$$ In case of collision with an obstacle on ground, the equation was: $$sum_n^{i=1}W_ia_s{cosalpha(1-sinphi_1)-{frac {C_1V^2sinphi}{gRcoseta}}-frac {1}{2}I_{TP} ( {frac {2kV_2} {d_1+d_2})-I_{AB}{frac{V^2}{Rr}} ( frac {pi}{2}-frac {pi}{180}phi_2 } = 0 $$ (2) As the angle of steering direction was increased, the critical travelling veloculcornerities of side sliding and dynamic side overturn were decreased. (3) The critical travelling velocity was influenced by both the side slope angle .and the direct angle. In case of no collision with an obstacle, the critical velocity $V_c$ was 2.76-4.83m/sec at $alpha=0^circ$, $eta=20^circ$ ; and in case of collision with an obstacle, the critical velocity $V_{cc}$ was 1.39-1.5m/sec at $alpha=0^circ$, $eta=20^circ$ (4) In case of no collision with an obstacle, the dynamic side overturn was stimuulcornerlated by the carrying load but in case of collision with an obstacle, the danger of the dynamic side overturn was decreased by the carrying load. (5) When the system travels downward with the first set of high speed the limit {)f slope angle of side sliding was $eta=5^circ-10^circ$ and when travels upward with the first set of high speed, the limit of angle of side sliding was $eta=10^circ-17.4^circ$ (6) In case of running downward with the first set of high speed and collision with an obstacle, the limit of slope angle of the dynamic side overturn was = $12^circ-17^circ$ and in case of running upward with the first set of high speed and collision <>f upper wheels with an obstacle, the limit of slope angle of dynamic side overturn collision of upper wheels against an obstacle was $eta=22^circ-33^circ$ at $alpha=0^circ -17.4^circ$, respectively. (7) In case of running up and downward with the first set of high speed and no collision with an obstacle, the limit of slope angle of dynamic side overturn was $eta=30^circ-35^circ$ (8) When the power tiller without implement attached travels up and down on the general slope ground with first set of high speed, the limit of slope angle of dynamic side overturn was $eta=32^circ-39^circ$ in case of no collision with an obstacle, and $eta=11^circ-22^circ$ in case of collision with an obstacle, respectively.