The main objective of this article was to investigate whether it is possible to detect with AE measurements a difference between the new and already used injection mold engraving inserts and what is their impact on the quality of the produced plastic parts. The used injection-mold engraving insert was not in operation for almost one year and was thus affected by surface corrosion. Experimental test results obtained with acoustic emission method on an unused and already used injection-mold engraving insert are presented. The investigation was mainly focused on analysis of the measured AE signals obtained from one resonant 150 kHy piezoelectric acoustic emission sensor mounted on the top of the tool. The AE signals were captured during injection-molding cycle. From these measurements we gained valuable information about the presence of corrosion on the tool steel surface.