We investigated experimentally the response of the fiber-optical refractometric sensor with semi-cylindrical plastic detection element under different polarization states of the input light. Our results demonstrate that the state of polarization of light in such sensor has a significant effect on the sensor response to external refractive index. This property can be exploited, in particular, for adjusting the form and linearity of the sensor response in situations when such adjustment cannot be achieved by modification of the sensor geometrical parameters and material constants.