The thermal poling method was utilized to create second-order optical nonlinearity in Pyrex borosilicate glass. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. The induced optical nonlinearity was found in a thin layer around 1.9μm under the anode surface with a magnitude as high as 0.24pm/V, comparable to that observed in fused silica samples. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ∼1.8μm under the anode edge and ∼0.3μm in width; while in post-annealed samples, no such etched trench could be observed. The effect of poling voltage on the magnitude of the induced nonlinearity was also studied, where the results showed that higher poling voltage resulted in higher nonlinearity with a threshold of ∼0.9kV.