The paper deals with a stress analysis of the existing tank trailer for bulk materials as well as with the effects of bulk materials on the tank trailer wall. Technical parameters: Volume 62m3, Max. working pressure 2 bar, Max. load weight 32 000 kg, Material EN AW-5083 0/H111. Designed according to AD 2000 Merkblatt. Analysis is based on extreme load conditions of the structure identified from the trailer working cycle. Based on its results, design optimization is made so as to eliminate the places with increased stress and, if possible to reduce the weight of the structure.