Abstract A liquid level sensing scheme based on leaky mode attenuation and a corresponding liquid level sensor based on a guided-mode–leaky-mode–guided-mode (GLG) fiber structure are proposed, which aim at the liquid whose refractive index (RI) is higher than that of the silica fiber. With mode expansion in terms of guided modes and leaky modes, theoretical analysis and simulations on the sensor are presented. The results, which are then verified by our experiments, indicate that the sensor offers not only an excellent linear response to the liquid level, but also a capability of discriminating the RI of the liquid.