<p><i>β</i><i>-</i>Glucan rich polysaccharides from <i>Ganoderma lucidum (G. lucidum)</i> possess significant bio-functional potential, yet their efficient extraction and purification remain challenging. In this study, six different extraction techniques were systematically compared for <i>β</i>-glucan yield and purity. Among them, alkaline extraction showed superior performance, while ultrasound and microwave methods demonstrated promising efficiency with reduced processing time. Based on these findings, a sequential ultrasonic-microwave-assisted alkaline extraction (S-UMAE) strategy was developed and optimized using response surface methodology (RSM) with central composite design. The effects of sonication time, microwave power, and microwave irradiation time on <i>β</i>-glucan yield and purity were statistically modeled, yielding high predictive accuracy (R² = 0.9980 for yield and 0.9960 for purity). The optimized conditions (110&#xa0;min sonication, 700&#xa0;W microwave power, 7&#xa0;min irradiation) produced 11.26% yield and 34.91% <i>β</i>-glucan purity, closely matching model predictions. The extracted polysaccharide (UMA) was further carboxymethylated to enhance solubility (from 1.9% to 82.54%), and structural characterization by UV-Vis, FTIR, and XRD confirmed successful derivatization and structural modification. Antioxidant activity, evaluated by the DPPH assay, demonstrated improved radical-scavenging capacity following carboxymethylation. Overall, this work demonstrates that S-UMAE combined with chemical derivatization is an effective strategy for obtaining high-quality, functional <i>β</i>-glucan polysaccharides from <i>G. lucidum</i> with enhanced physicochemical and bioactive properties.</p> Graphical abstract <p></p>