Abstract: The present paper reports the authors first finding concerning the method of controlling a slight interfacial reaction in SiC_P/6061Al composite fabricated by squeeze casting. Reaction mechanism and reaction effect on the Youngs modulus of the composite were studied. The results indicate that the interfacial reaction products are isolated small particles of MgAl₂O₄. The principal supply of oxygen in reaction is the residual thin SiO₂ layer around the as received SiC_Particles. The existence of reaction product found in the study has a beneficial effect on the Youngs modulus enhancement of the composite.