Nowadays, it can be seen an increasing use of microprocessors in electric motor monitoring systems. Such systems are often used to measure the basic operating parameters of the electric motors, like current, voltage, active and reactive power. The existing measuring methods require relatively high sampling rate for signals measurement and a relatively high computational power for processing the acquired data. The paper presents a new measuring method and calculating procedures to achieve the parameters of motor mentioned above. The method consists in parallel sampling of current and voltage signals with a very low sampling rate of only 8 Hz. Calculation formulas, used in this method, are relatively simple that allows their application in simple and cheap microprocessor systems. The paper presents the theoretical basis of the measuring method and processing algorithms. The block diagram of microprocessor measuring system (with a microcontroller ATMega 128), and the calculation algorithm of the method are presented. Laboratory tests of a low-power electric motor was performed and the results achieved by new method compared with the classical one.