The literature focusing on the transverse mechanical properties of single fibers is very sparse compared to those related to longitudinal properties. An original characterization method is proposed herein, relying on a micro mechatronics device to implement a transverse compression test which is monitored using 2D full-field measurements. This is shown to allow for the identification of the transverse elastic properties of a single fiber. The method is used, at first, on a bio-based polymer monofilament (PA11) which is assumed to have regular and controlled dimensions and geometry. The transverse elastic modulus is identified to be equal to approximately 1500 MPa and the longitudinal modulus 2150 MPa. The proposed method is then used to investigate the transverse compressive behavior of contrasted natural fibers, such as beard hair (protein-based) and sisal fibers (polysaccharides-based) which have more complex shape and/or internal structure. This paper gives for the first time the compressive force displacement curves as well as the monitoring of the shape of the cross-section during the loading.