Abstract: The first experimental system fabricated by the authors for oil/gas two-phase flow in hilly terrain pipelines is described, which is connected sequentially by a number of test sections of different inclinations.Complex flow characteristics are observed to be different from those flowing individually in straight pipes of the same inclinations. The most remarkable difference lies in the flow patterns formed. For example, as the oil/gas flow passes through the down-elbow part of the pipeline, new liquid slugs can be formed, while passing through the up-elbow part, the originally existed slugs will disappear. And, when liquid slug passes through the hilly terrain pipeline, some of its characteristics such as its frequency and liquid slug length may change even if the slug flow does not disappear. The experimental results obtained in this paper are important for the further theoretical study as well as the designs of oil/gas transportation pipelines and the separator.