In a changing and uncertain environment, the psychological contract becomes more important. This research attempts to explain of the degree of fulfilment of the psychological contract has an effect on solidarity behaviour of employees. Just as the psychological contract, solidarity behaviour is becoming more important. Employees have increasing responsibility for the quality of work and employers expect that employees work together and focus on mutual efforts to achieve the goals of the organization. A vignette-study, including a questionnaire with descriptions of specific situations, is used enabling an systematic and adequate analysis. Results support a positive effect between the degree of fulfilment of the psychological contract and organization solidarity. Theories of social exchange and justice play an important role in the explanation of this relationship. This finding shows that the psychological contract may be an important tool for the management of an organization to influence behaviour of employees. A finding of great value for the management of organizations.