The global climate change poses significant negative impacts on the sustainable development of human society and the safety of civil infrastructures, especially those in cold regions. Effective climate change mitigation requires both reductions of greenhouse gas (GHG) emissions and withdrawal of atmospheric carbon dioxide (CO2) to achieve the net zero emissions goal. The use of biochar as a soil amendment to both reduce GHG emissions and promote CO2 removal was proposed as a global strategy for climate change mitigation and has been intensively studied over the past decade. However, the effect of biochar addition on the physical and mechanical properties of cold regions engineering soils is rarely investigated and less understood. In the present study, the physical properties and frost heave characteristic of Lanzhou loess modified with biochar were experimentally studied. A series of laboratory tests were conducted on the loess and biochar to characterize their physical properties. And, six frost heave tests were carried out via a temperature-controlled system to quantify the behavior of the biochar-amended loess, considering the influences of the particle size and mass content of biochar. The results suggest that biochar can reduce the maximum dry density, increase the optimum moisture content and consistency limits of the tested loess, and the effect is related to the amount and particle size of biochar. Temperature gradient is the driving force for the migration of pore water. The largest increment in water content generally agrees well with the frost penetration depth. The addition of biochar could potentially decrease the amount of frost heave of the loess. These findings can provide valuable insights into the frost heave behavior of biochar-amended soils, as well as promote the application of biochar for frozen soil engineering and climate change mitigation.