To study the effect of the vent and dense surface of the phophate-bonded investment on the castability of a non-precious alloy used in PFM restoration, one-ended polypropylene straw patterns of 0.15mm thick, 5mm radius. 10mm-high were cast with Vera Bond. The following results were obtained. 1. Thin patterns could be cast completely with a non-precious alloy. 2. No difference in the castability was found among the patterns with vent, chill vent and with out vent. 3. Dense surface of the phosphate-bonded investment had no effect on the cast ability of a nonprecious alloy.