This paper describes a observer of direct current motor's (DC motors) parameter based on particles swarm method allowing to define the parameters values set and variables state in real time. During the electric motor operation the values characterizing its current state, for example, the resistance and inductances of the field winding and armature coil change over a wide range and are inaccessible for direct measurement therefore their indirect definition by means of observers is necessary. The current state of the working electric motor at the same time is defined by computer processing easily of measurands -voltage and currents of motor windings, by using of its mathematical model and estimation methods. The mathematical processing algorithm, features of settings, performance and some other results of the research are presented in this article. The results of this work can be used in the design of sensorless DC drives. The estimated DC motor parameter's can be used for control, monitoring and diagnostics of DC drive technical state. For check of serviceability and accuracy of the PSO method the computer motor model received on the basis of the equations of the generalized electrical machine was used. State estimation results of the working electric motor P-12 type confirmed validity of the offered approach.