A heat-resisting diatomite protection tube, using diatomite as a main component, was manufactured through an extrusion molding of ceramic slurry in different component ratios. And its mechanical strength, carbon analysis and microstructural non-homogeneity were investigated. After fixing $60wt\%$ of porous diatomite whose particle size was $50~100;{mu}m$, the optimum mixture ratio with composition variables by changing $1;wt\%$ of each component that was silica sol$(4.3~7.3;wt\%)$ as an inorganic binder, CMC (Sodium CarboxyMethyl Cellulose $(6~9;wt\%)$) as an organic binder and paper powder$(4.7~7.7;wt\%)$ was obtained. As a result of the investigation on a composition containing $60;wt\%$ diatomite, $5.3;wt\%$ silica sol, and $7;wt\%$ CMC, a heat-resisting protection tube that could be used as a molten steel probe for measuring the temperature and components of molten steel was developed. The bending strength, compressive strength, and elastic modulus of the protection tube developed, that contained $le2.3;wt\%$ carbon, were 7.1 MPa, 7.5 MPa, and 1090 MPa, respectively.