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.

1. A method of precision casting titanium or titanium alloy comprising the steps of:

mixing a binder with at least one of M.sub.g O powder and Al.sub.2 O.sub.3 powder to form an investment compound, said at least one of M.sub.g O and Al.sub.2 O.sub.3 powder having a grain size of 100 .mu.m or less and being 20-40% by weight of the investment compound;
kneading the investment compound with water;
embedding a wax pattern in the investment compound;
allowing said water to react with said investment compound to expand said investment compound; and
firing the investment compound with the wax pattern embedded therein to effect a lost-wax process an d expand a mold thus formed;
whereby expansion of said mold compensates for dimensional errors caused by shrinkage of the titanium or titanium alloy.