The flag is one of the most important symbols of Olsztyn. It is in the shape of a rectangle and of a blue colour. At the top of the flag, near the shaft, there is a yellow shell, and in the lower part runs a wavy strip of white colour along the entire length. These colours are not random. In fact, they refer to the colours of the city's coat of arms. White is the colour of the emblem, that is, of St. James’s garments.

The colour blue relates to the area of the coat of arms and yellow to its other elements such as: cane, soft leather boots with upturned toes (ciżmy), nimbus and a shell. The shell plays a special role in the symbolism of the Flag of Olsztyn. It is not only a distinguishing characteristic sign to other municipal flags, but also a symbol of the pilgrims, which is an important attribute of St. James. Therefore, the shell is the pilgrims’ sign of St. James’s international route and appears in its labelling. The wavy strip at the bottom of the flag is a reference to the location of Olsztyn by the Łyna River. The flag's pattern was created after the first local elections in 1990 and was created by Jacek Skorupski.