Abstract:【Objective】Rapeseed (Brassica napus L.), one of the most important oilseed crops in China, is sensitive to magnesium (Mg) deficiency. The Yangtze River Basin is the main planting area for winter oilseed rape in China, and the climatic characteristics of the region with simultaneous rain and heat, high-intensity planting patterns and long-term unbalanced fertilization have led to serious depletion of soil magnesium. Investigating the impact of different Mg fertilizers on seed yield and quality of rapeseed in China’s main winter oilseed rape production areas provides a theoretical basis for the rational application of Mg fertilizers in rapeseed cultivation. 【Method】Between 2019 and 2020, 56 field trials were conducted in the main rapeseed-growing regions in China. The trials followed a one-way experimental design, with three distinct Mg fertilizer treatments: no Mg fertilizer (CK), magnesium sulfate at the rate of 45 kg·hm-2 (Calculated as MgO, the same as below) (MgSO4·H2O, referred to as MgSO4), and magnesium chloride, also at the rate of 45 kg·hm-2 (MgCl2, referred to as MgCl2). The response of rapeseed to the two Mg fertilizers was evaluated by analyzing the rapeseed yield, yield components, oil, protein, sulfide content and fatty acid fractions. 【Result】The results revealed that the application of both MgSO4 and MgCl2 significantly increased rapeseed yield by 14.1% and 11.8%, respectively. The increase was primarily attributed to an increase in pod number per plant and seeds per pod. MgSO4 and MgCl2 increased the pod number per plant by 10.2% and 8.2%, and the seeds per pod by 3.9% and 2.4%, respectively. Analyzing the relationship between soil Mg content, sulfur content and yield increase resulting from Mg application indicated that the increase in seed yield was mainly associated with soil Mg content but not soil sulfur. The addition of MgSO4 and MgCl2 resulted in an 11.8% and 8.7% increase in seed Mg content (relative to no Mg application treatment), respectively. However, Mg accumulation was similar in both Mg application treatments. Additionally, the application of Mg fertilizer significantly improved rapeseed quality by increasing oil, oleic acid, and linoleic acid content by 5.5% and 4.8%, 8.3% and 7.7%, 7.8% and 11.4% for MgSO4 and MgCl2, respectively. Meanwhile, stearic acid, palmitic acid, and erucic acid contents were decreased by 4.60% and 26.1%, 7.5% and 13.9%, and 33.2% and 24.1% for MgSO4 and MgCl2, respectively. Although the application of MgSO4 resulted in a significant increase in sulfide, it remained below the national limits for edible rape oil and feed cake meal for double-low oilseed rape. 【Conclusion】In the main winter oilseed rape production areas in China, the application of MgSO4 and MgCl2 can significantly increase rapeseed yield, with MgSO4 having a slightly greater effect compared to MgCl2. Magnesium application also increases the Mg content and improves the oil quality of rapeseed by increasing the content of oleic acid and linoleic acid while reducing stearic acid and palmitic acid contents. These synergistic improvements contribute to both yield and quality enhancement.