<p>To address the limited reinforcement efficiency of enzyme-induced calcium carbonate precipitation (EICP) caused by insufficient nucleation sites, this study introduces xanthan gum (XG) to immobilize the enzyme and promote the CaCO₃ nucleation. A series of unconfined compressive strength (UCS) tests and ultrasonic oscillation tests were conducted to evaluate the effects of XG on the mechanical behavior and slaking resistance of biocemented sand. The nucleation and cementation mechanisms of XG addition were clarified through scanning electron microscopy with energy-dispersive spectroscopy and X-ray diffraction. The results demonstrate that as the XG concentration increased from 0 to 2 g/L, the UCS increases from 121.10 to 231.05 kPa, showing an increase of 90.8%. At the same time, the average slaking index decreases from 2.588 to 1.323. The enhancement is attributed to the increased viscosity of the enzyme solution with XG addition, which improves solution retention in low-energy sites. In addition, the negatively charged carboxylate groups on XG enhance Ca²⁺ adsorption, creating more nucleation sites and promoting targeted precipitation of CaCO₃ at particle contact points and interfaces. This study confirms that biopolymer-assisted nucleation can improve both the strength and slaking resistance of biocemented sand, providing a basis for promoting biocementation technologies in applications such as erosion control and hydrological engineering.</p>