This paper presents a process and result of reduction of the dimensions of microstrip square antenna shorting pins or loading circuit inserted to the antenna comparing to the conventional one. The slits applied to the antenna to generate the circular polarization properties of the antenna. This antenna is called as a Loading Circuit Microstrip Slit (an LCMS) antenna. The antenna is designed to work at a frequency of 435.9 MHz. This frequency is a part of UHF band of nano-satellite operation. From the simulation results, by adding a loading circuit of chip resistor 1 Ohm instead of the shorting pin, the overall size of an LCMS antenna will be reduced and the bandwidth of antenna becomes wider. For frequency of 435.9 MHz, the return loss of antenna is -21.445 dB, the bandwidth is 44.13 MHz, axial ratio is 2.9 dB, and the total size reduction of an LCMS antenna is equal to 338.46%.