The results of the testing of the EULER software package for energy conservation during the motion of conservative mechanical systems are presented. In conservative mechanical systems, at any point in their motion, the sum of the potential and kinetic energies should remain constant. To test the accuracy of energy conservation in calculating the motion of conservative systems, the following examples were compiled in the EULER:

• Example 1. One body connected by a rotational hinge, in the field of gravity.
• Example 2. Three bodies connected by rotational hinges, in the field of gravity.
• Example 3. An unbalanced gyroscope in the field of gravity.

In all the presented examples, in the process of motion of conservative mechanical systems, the relative error of conservation of the total energy is calculated. This error depends on the step and time of numerical integration.