The effect of magnetic field on shear stress of disklike nematic liquid crystalline polymers (LCPs) is analyzed with the extended Doi theory in which the molecular shape parameter is defined at negative one. The evolution equation for the probability function of the LCP molecules is solved without any closure approximations. It can be seen that the shear rate regions of the sign changes of the time-averaged first normal stress differences are completely contrary with those conclusions achieved for the rodlike LCPs.