The patrol icebreaker “TESHIO” was built and delivered to the Japan Maritime Safety Agency in Autumn 1995. Full-scale trials in ice were conducted at the Sea of Okhotsk in February, 1996. Several kinds of test were performed in order to confirm her performance such as continuous ice-breaking, ramming and stopping performance, turning capability and zigzag course manoeuvrability, and coordinated ice-breaking operation together with the patrol icebreaker “SOYA”. While her design and construction were in process, series of model test were carried out both in ice and in ice-free water as the joint research project between Ship Research Institute, Ministry of Transport and NKK Corporation. At the ice model basins of the two organizations, comprehensive model tests in ice were conducted which included resistance and self-propulsion tests in various ice conditions, ramming and turning tests in level ice. This paper describes the results of model and full-scale tests of “TESHIO” and their correlation for both continuous ice-breaking and ramming performance. In order to predict the required BHP for the continuous ice-breaking in level ice, the propulsion coefficient was decomposed into three parts which denote effects of open water characteristics, overload and propulsor/ice interaction, respectively. The thrust deduction coefficient obtained from towed propulsion tests in ice showed very good agreement with that from overload tests in ice-free water. The predicted BHP showed good agreement with the full-scale results when the effect of propulsor/ice interaction was taken into consideration. A prediction formula for ramming penetration distance was devised using an energy-based method. Correlation of both the model and full scale data to the prediction results showed that thrust loss due to the propulsor/ice interaction and the automatic overload protection control of the main engine had much influence on the prediction of ramming performance.