The statistical properties of the spatial derivatives of the Stokes parameters for a random polarization field are studied. Based on the Gaussian assumption for the electric fields, the six-dimensional joint probability density function for the derivatives of the Stokes parameters is obtained from the statistics of the derivatives of the random polarization field. Subsequently, three two-dimensional probability density functions of derivatives of each Stokes parameter and the corresponding six marginal probability density functions are given. Finally, the joint and marginal density functions of the magnitude of the gradient of Stokes parameters are also derived for the first time, to our knowledge. © 2010 Optical Society of America.