Orientation: The relationship between psychological capital (PsyCap) and organisational citizenship behaviour (OCB) is important to establish especially in the South African public hospitals where the quality of healthcare services have been reported to have deteriorated.Research purpose: The purpose of this study was to examine the relationship between psychological capital and organisational citizenship behaviour among nurses in the public hospitals.Motivation for the study: There is crisis in the public nursing sector as nurses are reported to be working under pressure as a result of increased workload and responsibilities beyond their scope of practice (in terms of doing the work that they are not trained for and more work than they can handle), in addition to rapidly changing work environments.Research approach, design and method: The present study follows a quantitative cross-sectional design using a questionnaire on a sample of 228 nurses from public hospitals in the Eastern Cape Province, South Africa.Main findings: The findings of the study confirm that psychological capital has a significant positive relationship with organisational citizenship behaviour.Practical/managerial implications: The study recommends management to recognise the area of OCB in the public hospitals and work in nurturing and retaining those nurses capable of displaying such behaviours.Contribution/value add: The study validates aspect of reciprocity of the Social exchange theory. Nurses with high levels of hope, self-efficacy, resilience and optimism showed reciprocity through the display of OCBs. The study also validates the aspect of job resources in eroding job demands from the Job demands resources model.