The policy and measures that alter forest harvest level can be greatly offset by the presence of harvest leakage. Our study has quantified the leakage rates in four Nordic countries when a range of harvest shocks are introduced. A partial equilibrium forest sector model named the Nordic Forest Sector Model (NFSM) with 31 regions is applied for the purpose of the study. The roundwood leakage rates range from 58% to 91% in Norway, 73% to 91% in Sweden, 75% to 107% in Finland, and 59% to 106% in Denmark within the tested range. The leakage rates for sawlogs can be over 100% when the leakage of both sawnwood production and sawlogs happens the same time, and they can also be small if synergistic effect is present. The extra-Nordic leakage dominates the harvest leakage if harvest changes in one of the studied Nordics countries, and the leakage of the sawlogs harvest is a combined result of leakage of the raw materials (sawlogs) and the leakage of the production (sawnwood), while the leakage of pulpwood harvest is solely a result of leakage of the raw materials (pulpwood). The substitution of pulpwood by harvest residues and black liquor is significant in bioheat sector when harvest of pulpwood change. Therefore, we highly recommend that extra caution should be taken if a climate action may affect the level of the forest harvesting, and the harvest leakage effect on domestic industries, international trading should be awarded in open markets.