This study investigated the selective adsorption mechanism of guar gum (GG), a green and efficient regulator, in the flotation separation of diaspore and kaolinite. Under a sodium dodecyl sulfonate (SDS) system, flotation tests showed that GG achieved a maximum flotation difference of 72.99% between the two minerals, along with an Al₂O₃/SiO₂ ratio of 9.47 and a selectivity separation index of 5.01. Contact angle measurements revealed that GG slightly reduced the contact angle of diaspore (by 3.56°) but significantly reduced that of kaolinite (by 14.51°), thereby enhancing the floatability contrast between them. Zeta potential tests confirmed strong GG adsorption on kaolinite and weak adsorption on diaspore, as the shift in kaolinite's isoelectric point after GG treatment was more pronounced than that of diaspore. Fourier transform infrared spectroscopy indicated that the strong adsorption of GG on kaolinite hindered subsequent SDS adsorption, whereas on diaspore, GG adsorbed weakly, allowing SDS to still adsorb effectively. XPS analysis further showed that GG had only minor effects on the Al peak shifts and Al content changes of both minerals, but significantly affected the Si peak shift and Si content on kaolinite surfaces, reflecting selective adsorption of GG onto kaolinite and specifically onto its Si sites. Consequently, during flotation, kaolinite is inhibited and sinks, while diaspore remains floating, enabling efficient separation of the two minerals.