[Objective] Soil structure is an important factor affecting movement of water, gas and nutrients, root growth, and soil biological activities in the soil. Reasonable tillage is an important farming practice to create soil structure favorable to crop growth. No-tillage has already demonstrated to improve soil structure and soil biodiversity in upland fields. However, so far few studies have reported effect of no-tillage on soil structure of paddy fields. This study was conducted to explore effects of no-tillage on the structure of a paddy soil in a rice-rapeseed rotation system.[Method] Based on a 4-year(2016-2019)tillage field experiment in the Dongting Lake area of North Hunan, effects of rotary tillage (RT) and no-tillage (NT) on soil pore structure of the plough layer (0-25 cm) of a paddy soil were investigated using the X-ray CT imaging technique. Soil aggregate stability was also evaluated using the Le Bissonnais fast wetting method.[Result] The soil organic carbon content of the top soil layer (0-5 cm) in the RT and NT treatments was 34.3 g·kg^-1 and 34.4 g·kg^-1, respectively, which were higher than those of the other soil layers. Compared with the plots under RT, the plots under NT had a slightly lower soil bulk density in the 0-5 cm soil layer (P>0.05), and significantly more>2 mm soil aggregate in the 0-5 cm and 5-10 cm soil layer. Tillage significantly affected soil macroporosity (>25 μm). Compared with the RT treatment, the NT treatment significantly increased soil macroporosity by 78% and 115% in the 0-5 cm and the 5-10 cm soil layer, respectively. Soil pore size distribution was also greatly altered by tillage practices. The NT treatment increased macroporosity of each of the pore size fractions in the 0-5 cm and 5-10 cm soil layers, especially increased the 300-500 μm macropores in the 0-5 cm soil layer and the 25-300 and 300-500 μm macropores in the 5-10 cm soil layer by 70.5%, 82.8% and 167.2%, respectively.[Conclusion] Our findings show that no-tillage in paddy field improves soil aggregate stability and increases macroporosity of the topsoil, which are beneficial to improvement of physical structure of the paddy soil.