Objective To evaluate the effects of firing numbers on the total opening pore volume（TPV）, translucency parameter（TP） and color of dental all-ceramic systems. Methods Specimens of three kinds of all-ceramics systems were made, i.e. heat pressed all-ceramic（IPS Empress Ⅱ）, alumina all-ceramic（In-Cream alumina blanks） and zirconia all-ceramic（Cercon CAD/CAM zirconia）. The specimens’TP, lightness（ΔL）, chroma（ΔC） and TPV after 1, 3 and 5
firings were measured and calculated by spectrophotometer and surface area/porosity system. The data were analyzed statistically using SAS 8.0 software. Results There were significant differences in TPV, TP, ΔL and ΔC for all-ceramic specimens at same number of firings（Palumina and zirconia for TPV（Pzirconia>alumina for TP and ΔL（Pzirconia for ΔC（PΔL and ΔC for a same specimen at different number of firings（P
