The interpolation basis formed data originating from boreholes. Assessment of interpolation errors of sulphur and ash contents was performed in points of seams sampled in underground mine workings using 5 interpolators: minimum curvature, inverse distance to a power, kriging modified Shepard's method and radial basis function. It was found that regardless interpolators used the interpolation errors are very high with mean relative absolute values of 34-157% and correlation between predicted and real values of studied parameters is very weak. The interpolated values quite often are burdened with a systematic error. Therefore, it can be accepted that visualizing spatial distribution of the sulphur and ash contents in coal seams contour maps prepared in the early stages of deposit exploration based on drilling data is groundless. The main reason of low accuracy of interpolation is the high variability of studied parameters and wide spacing of boreholes. Additional factors lowering the accuracy of interpolation are heterogenous spatial distribution of sulphur and ash contents in the seams as well as significant contribution of the random component to the total variability of the parameters dealt with.