In this paper an analytic method of study the dispersion characteristics of an open thick microstrip is presented. By the help of the hertzian vector it was found the integral equation for the current distribution and the transmission coefficient. From the numerical results it is shown that the attenuation constant due to the conductor loss is less in the rounded edge microstrip than in the rectangular one. For the current distribution the transverse current was at least ten times less the longitudinal one. So to study an open thick microstrip we have good approximation by using only the longitudinal current.