In this thesis, linear control systems with partly-quantized feedback have been studied. First, linear systems with partly-quantized feedback are defined as systems that some of their feedback signals are quantized and then transmitted to the controller while the rest of the signals are not quantized and directly available to the controller. Quantization regions are assumed to be rectilinear. It is shown that by observing the exact signals, controller can find a moving hyperplane in quantized signals space containing the true values of the quantized signals, using the intersection of this hyperplane and the quantization region and solving a min-max problem, a better approximation for quantized signals can be found. To obtain this approximation, first an algorithm is developed to find the extreme points of the aforementioned intersection and then it is shown that the problem of finding the approximation is the same as the problem of finding the smallest enclosing ball of a set of points which can be found by extreme points of the intersection and system properties. It is proved in theory that using this approximation in linear controller, better results are obtained and a smaller invariant region around origin can be determined. Numerical examples are given to show the effectiveness of the method.