This research has an objective to analyze the effect of type of sand dust in a casting process to sand mold 'ร attribute. Some old sand dust in this research were recycled from sucking system in a casting process that uses the sand dust for a material in the process. Also this process needs a Bentonite for a meterial of modeling sand. เท this research, the sand dust is qualified to three types. Type 1 is the roughest sand dust which have an average value of size or AFS No. (AMERICAN FOUNDRY STANDARD NUMBER) of 90.7 and a 15.5 percent of the Active clay. Type 2 is the moderately rough sand dust which have an average value of size or AFS No. (AMERICAN FOUNDRY STANDARD NUMBER) of 112.4 and a 23 percent of the active clay. Type 3 is the fine sand dust which have an average value of size or AFS No. (AMERICAN FOUNDRY STANDARD NUMBER) of 190 and a 43.6 percent of the active clay. The research results from blending of each type of sand dust with the recycled molding sand in a 5-kilogram mill. The component is 100 part of weights of recycled molding sand, Seacoal in the propertion of 0.1 per 100 part of weights of recycled molding sand, Bentonite, each type of new sand dust and water in different propertions. In the process, the quantity of sand dust is between 1 and 9 percent of the total component and the researcher controls in 12 ± 0.5 percent of the Active clay and between 3.0 ± 3.4 percent of the moisture value of blended sand dust. Finally, the researcher tests the attributes of blended sand dust that include the compressive strength 1 percent of compactability 1 permeability, volatile matter, AFS No. and percent of total clay. In the research, the researcher found that the type of sand dust effects to modeling sand ‘s attributes in 2 points. In the firstpoint, if the sand dust 'ร quantity increases, the compressive strength, percent of compactability and permeability decrease but volatile matter, AFS No. and percent of total clay increase. In the last point, if the sand dust 's size increases (AFS No. decreases) the compressive strength , percent of compactability and permeability increase but the percent of total clay decrease.