Bonding of resin to cast alloy has traditionally been provided by mechanical retention. But, chemical bonding methods such as silicoating, tin plating, heat treatment, application of 4-META adhesives, have been developed to overcome the problems of the mechanical bonding methods. Silicoating has been used availaby in fixed prosthodontics, but is also reported to be used in removable prosthodontics. The aim of this study is to measure the tensile bond strength between resin and metal, and compare the effect of the type of metal and the grain size of the aluminum oxide on the bond strength, after metal surface roughening, coating of the opaque resin, and curing of heat-curing resin were performed. The test groups were divided into 4 groups according to the cast alloys and the aluminum oxide particles used. Group 1 : Type 4 gold alloy(DM66) blasted with $$50{mu}m;Al_{2}O_3$$ Group 2 : Type 4 gold alloy(DM66) blasted with $$250{mu}m;Al_{2}O_3$$, Group 3 : Co-Cr alloy(Nobilium) blasted with $$50{mu}m;Al_{2}O_3$$ Group 4 : Co-Cr alloy(Nobilium) blasted with $$250{mu}m;Al_{2}O_3$$ * 10 test specimens were made on each group. The specimens were thermocycled, and Instron Universal testing machine was used to measure the tensile bond strength of the finished specimens. The results were as follows : 1. Bond strengths showed that the group of gold alloy blasted with $250{mu}m$ aluminum oxide particle had higher bond strength, and the group of gold alloy blasted with $50{mu}m$ aluminum oxide particles had lower bond strength than any of the other groups. 2. Gold alloy had significantly higher bond strength when blasted with $250{mu}m$ aluminum oxide particles than $50{mu}m$, but. Co-Cr alloy showed no statistically significant difference between the two particle sizes. 3. When blasted with $50{mu}m$ aluminum oxide particles, Co-Cr alloy showed significantly higher bond strength than gold alloy. And, when blasted with $250{mu}m$ aluminum oxide particles, gold alloy had significantly higher bond strength than Co-Cr alloy. 4. On the examination of the fractured sites, only the group of Co-Cr alloy blasted with $50{mu}m$ aluminum oxide particles showed a part of residual opaque resin, but all the samples of the other groups fractured between the resin and the metal.