With the growing awareness of environmental impacts of land degradation, pressure is mounting to improve the health and productivity of degrading soils, which could be achieved through the use of raw and modified biochar materials. The primary objective of the current study was to investigate the efficiency of pristine and Mg-modified rice-straw biochar (RBC and MRBC) for the reduction of greenhouse gases (GHG) emissions and improvement of soil properties. A 90 days' incubation experiment was conducted using treatments which included control (CK), two RBC dosages (1% and 2.5%), and two MRBC doses (1% and 2.5%). Soil physico-chemical and biological properties were monitored to assess the effects due to the treatments. Results showed that both biochars improved soil physicochemical properties as the rate of biochar increased. The higher rates of biochar (RBC 2.5 and MRBC 2.5) particularly increased enzymatic activities (Catalase, Invertase and Urease) in comparison to the control. Data obtained for phospholipid fatty acid (PLFA) concentration indicated an increase in the Gram-negative bacteria (G-), actinomycetes and total PLFA with the increased biochar rate, while Gram-positive bacteria (G+) showed no changes to either level of biochar. As regards fungi concentration, it decreased with the biochar addition, whereas arbuscular mycorrhizal fungi (AMF) showed non-significant changes. The release of CO 2 , CH 4 and N 2 O showed a decreasing trend over the time. CO 2 cumulative emission decreased for MRBC 1 (5%) and MRBC 2.5 (9%) over the pristine biochar treatments. The cumulative N 2 O emission decreased by 15–32% for RBC 1 and RBC 2.5 and by 22–33% for MRBC 1 and MRBC 2.5 as compared to the control, whereas CH 4 emission showed non-significant changes. Overall, the present study provides for the first-time data that could facilitate the correct use of Mg-modified rice biochar as a soil additive for the mitigation of greenhouse gas emission and improvement of soil properties. • SEM-EDX analysis showed that carbon content decreased while Mg content increased after modification. • RBC and MRBC increased the total PLFA. • Enzymatic activities increased as the rate of both biochar increased. • N 2 O emission significantly decreased by both biochar. • MRBC decrease CO 2 emission by 5% and 9% over RBC at both levels. [ABSTRACT FROM AUTHOR]