In order to assess the characteristics with respect to surface strength of thin hard coatings of the Micro Slurry-jet Erosion (MSE) test which we have developed, the erosion behaviors of PVD TiN coating were studied. The MSE tests were conducted impacting a slurry-jet consisting of angular alumina particles with an average size of 1.2 μm or 41 μm, and spherical alumina particles with an average diameter of 3 μm, perpendicular to the specimen surface. The variations of the eroded surface profiles and the erosion depths were measured, and the eroded surfaces were observed using SEM, AFM and TEM. The erosion rates and the morphology of the eroded surface depend strongly on the size and shape of the erodent particles. For tiny angular particles, the main erosion mechanism is impact fatigue and sub-micro-cutting, while plastic deformation and micro-crack propagation due to fatigue are the main erosion mechanism for tiny spherical particles. On the contrary, in the case of large angular particles, brittle fracture followed by cutting due to large impact forces is the main characteristic. The depth to which the impacts of particles have an influence depends on the size and shape of the particles; the range of influence is from several tens of nanometers for tiny particles to several hundreds of nanometers for large angular particles. From these findings, it is concluded that the MSE test can be used to evaluate the properties related to various strengths by selection of the appropriate erodent particles.