<p>Calcareous sand is commonly used as filling materials for the construction of infrastructure foundations in island or coastal engineering projects. However, its susceptibility to particle breakage and high compressibility threaten the safety and stability of geotechnical structures built on calcareous sand foundations. Enzyme induced carbonate precipitation (EICP) technique has shown great potential for the soil reinforcement. To investigate the compressive characteristics and deformation mechanism of EICP-treated calcareous sands under high-pressure conditions, a series of one-dimensional compression tests were conducted at vertical pressures of up to 70&#xa0;MPa. Through variations on the initial dry density and cementation level, the compressive behavior, particle gradation and microstructure were analyzed and discussed. The results revealed that the dominant deformation mechanism transformed from particle breakage to particle aggregation with increasing the carbonate content (<i>C</i>_<i>c</i>). After high-pressure compression, the EICP-treated calcareous sand was composed by newly graded aggregates bonded by particles of various sizes. The “grade-jump” of the original sand particles within the bonded aggregates led to the particle size distribution curve shifting toward the aggregation region after compression. When a certain threshold of <i>C</i>_<i>c</i> was achieved, a considerable proportion of carbonate bonds remained intact and fractured sand particles coexisted within large-sized bonded particle aggregates. The EICP-treated calcareous sand could maintain the overall structural stability under high-pressure conditions.</p>