The aim of this paper is to analyze effect of operating conditions (duration, flow rate, temperature and transmembrane pressure) on the purity ratio, colour changes and turbidity changes of the permeates obtained by ultrafiltration (UF) and nanofiltration (NF) applied for the clarification and purification of sugar syrup solution. The analysis was based on the results of experiments performed in batch conditions, with 2 L of the initial syrup, on two types of the flat, cross-flow membranes: polyethersulfone for the UF process, and polyamide for the NF process. The plan of the experiments was in accordance with a full factorial design, and the 12-parameter polynomial proved adequate for data processing in all the examined cases. It was found that the response surfaces do not have extremes. However, the conclusions towards optimization of operating conditions, in most cases, were as follows: (1) process duration could be shortened, (2) flow rate should be kept at the lower boundary and (3) transmembrane pressure should be kept at the upper boundary of the investigated experimental space. Temperatures in the previous stages of the process mostly determined temperature at separation. The higher the temperature at separation, the lower the effect of separation.