The composition of fatty acids and sterols of Crangon crangon abdomen muscle was determined during two periods in the year 2010/2011. For determination of lipids classes, especially of fatty acids and sterols, high performance liquid chromatography with a laser light-scattering detector and gas chromatography–mass spectrometry were applied. Diversity and variety of saturated and unsaturated fatty acids was the highest during the spring period. Twenty-seven free fatty acids with from nine to 24 carbon atoms were determined in the spring periods. Among this fraction, 14 saturated and 13 unsaturated fatty acids (eight mono- and five polyunsaturated) were present. Only seven saturated and four unsaturated free fatty acids (14:2, 17:1, 16:1 and 18:1) were identified in December 2010. Arachidonic acid (20:4) and eicosapentaenoic acid (20:5) were detected in these two periods, and during the spring season an additional essential fatty acid—docosahexaenoic acid (22:6)—was present, which was not detected in the winter period. The number of identified sterols was correlated with phytoplankton, which was abundant during April 2011. Also, the sterol fraction in winter periods was very poor—only cholesterol was detected.