An investment compound for use in a precision casting mold comprises MgO powder and Al.sub.2 O.sub.3 powder as main constituents in such a manner that the MgO powder and/or the Al.sub.2 O.sub.3 powder are or is in the range of 100 .mu.m or less in grain size and of 10% or more in weight precent, whereby even when a high-temperature active casting material such as titanium is used, the material provides a casting having a very beautiful surface with no bubbles formed therein and can positively compensate for shrinkage due to the solidification of cast material in a lost-wax process and can advantageously provide the casting at lower prices.