We report on optical fibers made from alkali glasses having enhanced third-order nonlinearity with respect to silica. The unique composition of these glasses with high alkali-ion content makes inducing second-order nonlinearity by electrical poling more convenient and effective. Using a femtosecond light source and voltages up to 600 V at room temperature, second-harmonic generation (SHG) in a non-phase-matched process with a highest output efficiency Eout of 0.019% (E = 1.12 × 10−6%) was observed. SHG is fully reversible with average mean rise and fall times of 3 s and 13 s. This makes alkali glass-based optical fibers good candidates for new devices with switchable and reversible nonlinearity.