Cutting performances of silicon nitride (Si 3 N 4 ) ceramic cutting tools with and without boride additive (2.5 vol% ZrB 2 or TiB 2 ) prepared by hot-pressing at 1500 • C were investigated. Due to the α-to β-Si 3 N 4 phase transformation and low densification temperature, boride-containing Si 3 N 4 ceramics with high hardness and high toughness were obtained. The turning tests showed that the effective cutting lengths of the Si 3 N 4 -2.5 vol% TiB 2 ceramic (∼2480 m) and Si 3 N 4 -2.5 vol% ZrB 2 ceramic (∼2200 m) were higher than the monolithic Si 3 N 4 ceramic (∼1780 m). As the toughness was improved while maintaining relative high hardness, the cutting performances of the boride-containing Si 3 N 4 -based inserts were improved by adding 2.5 vol% ZrB 2 or TiB 2 . The improved cutting performance indicated that the boride-containing Si 3 N 4 ceramics are expected to be used in the field of ceramic cutting tools.