Abstract: The pore size distributions (PSDs) of natural loess and remolded loess before and after stress path tests are measured by means of the mercury intrusion porosimetry (MIP) tests, and the relations between PSDs and macro-mechanical behaviours are analyzed. The results from MIP tests indicate that the PSD of remolded loess is similar to that of natural loess before stress path tests, both of which exhibit dual-porosity structure. The PSD of natural loess with w=15% is similar to that of the corresponding remolded loess after the same constant water content triaxial stress path tests, while the PSD of saturated natural loess is different from that of the saturated remolded loess after the same consolidated undrained triaxial stress path tests. The pores influenced by stress are inter-particle pores. The volume of the inter-particle pores after constant water content conventional triaxial compression (CTC) tests and reduced triaxial compression (RTC) tests decreases and increases respectively. The volume of the inter-particle pores after consolidated undrained RTC tests is greater than that after consolidated undrained CTC tests under the same consolidation stress. After the constant water content CTC tests under consolidated stress of 50 kPa which is lower than structural yield stress, the shear plane does not appear in natural loess and the difference of PSDs at different positions of the samples is not great. The macro mechanical characteristics are investigated from the micro point of view according to the difference of PSD between natural loess and remolded loess after the same stress path tests. The research result indicates that cementation bonds, capillary bonds and inter-particle void ratio play important roles in strength and deformation of the samples.