The paper presents experimental results of the work conducted to improve the adhesion between alumina ceramics and urea-urethane elastomer in the interpenetrating phase composites (IPCs), in which these two phases are interpenetrating three-dimensionally and topologically throughout the microstructure. Measurements of the contact angle, surface roughness, and shear tests were used to evaluate the effectivity and select the quantity of a silane coupling agent and the ceramic fabrication method. The tests were conducted using samples of dense alumina ceramic obtained by three- or four-step methods. In the four-step process, hot isostatic pressing (HIP) was applied additionally. As a result of the coupling agent coat and HIP application, the ceramic substrate wettability by the elastomer was improved. The water contact angle was reduced from 80 to 60%. In the next step, porous ceramic preforms were fabricated using HIP sintering and a solution of silane coupling agent treated their surface. The composites were produced using vacuum-pressure infiltration of porous alumina ceramics by urea-urethane elastomer in liquid form. The influence of the coupling agent application on the microstructure and mechanical properties of the composites was estimated. The microstructure of the composites was identified using SEM microscopy and X-ray tomography. As a result of using the coupling agent, residual porosity decreased from 7 to 2%, and compressive strength, as well as stress at a plateau, increased by more than 20%, from 25 to 33 MPa and from 15 to 24 MPa, respectively, for the composites fabricated by infiltration ceramic preforms with 40% of porosity.