Thermally sprayed deposits have layered stracture composed of individual splats. The individual splats have quenchin microstruture of quasi-stabl prferred fine grains. Howerer, this fine-grained microstructure of the deposlts is usually not reflected by improved performance of the deposits bvecause a layered structure with two-dimensional vnids occurs between lamellar interfaces. The microstructure of the thermal spray deposits with the emphasis on the layer structural parameters is reviewed. Conventionally. one of the most common quantitative parameters uased to characerize the mierostracruter of the thermally sprayed deposits is the porosity, measured by different methods. However, it is illustrated that the relationships between propterties and porosity for bulk porous materials processed by conventional processes cannot be applled to thermally sprayed deposits owing to the two-dimenslonal char-acteristics of vodis. The total porosity in the depesists is not meaningfol from the viewpoint of prediction off the deposit properties. An idealfzed stracaral model and related parameterx, imstedad of porosity, are proposed to characterize quantitatively the microstructure of the thermally sprayed deosit. the retationships between the properties and the stturchural parameters are preseted for the plasma-sparyed ceramid deposits based on the proposed microstructure model. the properties include the Young's modulus. fracture toughmess, erosion resistance, and thermal conductiveity of the plasma sprayed ceramic deposis. The correlations of theocetical relationships with reported expertimental data are disenssed. An agreeement of theoretical with observed values suggests that the lamellar structure of the deposit with limited interace bonding is the dominant factor controling the performance of the deposit.