This paper presents the processing of the data from the precise levelling measurements in the seismic active area of the Skopje valley. Precise levelling results are affected by the Earth’s gravity field, to eliminate the effect of the gravity field gradient, corrections need to be applied in processing of precise levelling data. For this purpose the processing of levelling data is performed together with GNSS coordinates and gravity data, which are acquired on a part of the state levelling network from first order, located on the territory of the City of Skopje. They are used for transformation of the height differences in the system of dynamic, orthometric and normal heights. Also other corrections are applied to observed levelling data to minimize the effects of known systematic errors.