Warp-knitted fabrics are textile assemblies which are composed of straight crimp less yarns. Unique characteristics of these fabrics such as their high formability are due to their specific internal structure. Formability of textiles in general is greatly affected by factors such as applied stresses during forming process. In this study, three-dimensional (3D) deformation induced in warp-knitted fabrics was evaluated. Bi-axial and tri-axial samples of commercially available warp-knitted fabrics constructed using glass fiber yarns were obtained. The samples were composed of 200 tex yarns in ±45° directions, however in tri-axial samples the tex of yarn in z-direction was 68. The constituent layers in the samples were connected together using chain stitch. Tensile properties of the samples were determined using ZWICK apparatus. Behavior of the fabric during deformation is affected by yarn inclination. The flat samples were formed into creaseless 3D hemispheres using a purposely designed and fabricated device. This device was successfully used to prepare 75 and 110 mm radii 3D hemispherical creaseless experimental samples. The prepared 3D samples were photographed using an 18 megapixels camera. A protractor was used to determine the changes in yarn inclination in the 3D samples by measuring the distance from the center of hemisphere from a given point. Also a geometrical model capable of predicting the change in inclination of each yarn in respect of other yarns was developed. Results pointed to existence of acceptable level of compatibility between theoretical and measured data. It was found that the compatibility between the model generated results with those obtained by experiments is more profound in case of 110 mm radii samples in comparison to 75 mm radii samples. It was observed that resistance to deformation due to applied external force in bi-axial samples irrespective of direction is similar. Additionally it was found that the resistance to deformation of tri-axial samples in 0° direction is less than that in ±45° directions. It was concluded that the elastic modulus of tri-axial fabrics is more than that of bi-axial samples, thus it was stated that resistance to deformation of bi-axial samples is considerably less than that of tri-axial samples. Key Words: warp-knitted fabric, 3D deformation, Forming, glass fiber, yarn inclination