The paper includes the following elements: the characteristics of diaries as the source of knowledge in social sciences, basic assumptions for the research based on diaries in the science of social policy, autobiographic contents in Polish research, methodological problems in the analysis of diaries. The analyses of diaries have a strong position in Polish tradition, especially in researching social questions and life condition of people. The leading role in this type of research was taken by the Institute of Social Economy, which worked out basic principles of studying diaries for the needs of social policy. These principles need modifying while new research perspectives appear in the science of social policy (ex. the perspective of life cycles). The research based on diaries is expected to include more deep methodological reflection. For the science of social policy diaries remain a valuable, yet too weakly utilised source of knowledge.