When a continuous-time system is sampled by use of a zero order hold, all stable poles are transformed into the unit circle. However, there is no simple relation between the zeros of a continuous-time system and its sampled version. This paper has derived sufficient conditions which guarantee that a continous-time system with zeros in the left half plane is transformed to a sampled system with zeros inside the unit circle for all sampling periods. The criteria shown in this paper are represented by coefficients of the partial fraction expansion of a continuous-time transfer function.