In this paper, for the first time, the tensile strength of water is directly measured using an optofluidic chip based on the displacement of an air-water interface deformation with homogeneous nucleation. When water in a microchannel is stretched dynamically via laser-induced shock reflection at the air-water interface, the shock pressures are determined by measuring the displacements of the deformed interface. Observation of the vapor bubbles is used as a probe to identify the cavitation threshold with a critical distance, and the tensile strength of water at 20 ºC is measured as -33.3 ± 2.8 MPa. This method can be extended to investigate the tensile strength of other soft materials such as glycerol, which is measured as -59.8 ± 10.7 MPa at 20 ºC.