Castability and loss of mass from Co-Cr castings after polishing had been evaluated. Casting systems of centrifugal and vacuum types and two types of phosphate- bonded investments were used. Cast plates were weighed before and after polishing (limit value of 100 ± 20nm was confirmed with AFM) to measure mass loss (%). Surface layer of cast specimens and porosity of investments was observed. Loss of mass of cast specimens and surface reaction layer was not influenced either by casting systems or by porosity of investments. Investments with more porous structure and centrifugal type casting system had shown significantly improved castability.