This study suggests a western boundary current instability generation mechanism for the ocean internal waves. A linear model describing this instability is developed, and an analytical solution is derived from a zero-order complex frequency--wavenumber relation. The real part of the relation represents a dispersion relation of the generated internal waves, and the imaginary part is an exponential growth rate. The dispersion relation describes the wave propagation characteristics, while the growth rate represents the instability properties. The theoretical results are used for the case of the Kuroshio east of the Luzon Strait. Based on the analysis, it is found that for the westward propagating disturbance, the Kuroshio west wing is unstable and the east wing is stable; while the reverse is true for the eastern propagating disturbance. The results are used to interpret satellite SAR images of the ocean internal waves, which were generated in the Luzon Strait and propagated westward. Reasonable estimates for the growth rate and propagation velocity are derived from a scale analysis of the Kuroshio east of the Luzon Strait.