The study was conducted in the experimental field of Dobrudzha Agricultural Institute on slightly leached chernozem. To clarify the effect of long-term application of main soil tillage on the mean weight diameter of dry structural aggregates (MWDd), long-term data were analyzed from the following treatments in a stationary field experiment: moldboard ploughing at 24-26 cm (MP), chiseling at 24-26 cm (CP), disking at 10-12 cm (DH), and no-tillage (NT). Over the study period (1994-2024), an overall reduction in MWDd was observed in the 0-10 cm soil layer for all tillage treatments. The most stable soil structure was maintained under CP and NT, whereas the application of MP and DH led to deterioration of the studied indicator. The results show that sustainable management of the surface soil layer requires limiting intensive tillage, maintaining plant cover, and increasing organic matter, which are key to stabilizing soil structure, reducing erosion, and preserving soil fertility. In the 10-20 cm layer, long-term NT application led to an improvement in MWDd. Under CP, satisfactory structural stability was maintained. Under MP and DH, the gradual degradation of soil structure over the long term may negatively affect soil water and air regimes. The NT treatment ensured the highest structural stability and improvement of MWDd in the 20-30 cm layer. Under CP and DH, soil structure was maintained with minimal loss of aggregate stability, while the MP treatment showed a continuation of the trend observed in the upper horizons toward destabilization of soil aggregates. Based on this long-term study and considering the soil type and climatic conditions of Southern Dobrudzha, conservation tillage practices (no-tillage and chiseling) can be recommended for the sustainable preservation of soil structure and fertility.