In the highly competitive business environment, family businesses represent the backbone of the economy in various countries; meanwhile, they face tremendous survival challenges. Knowledge, particularly tacit knowledge, is the key to organisational survival because the hard-to-imitate characteristics could create value and technology innovation. However, it is challenging for family businesses to obtain tacit knowledge because it resides in people’s minds; and compared with sharing, people prefer hiding it for self-protection. In recent years, knowledge hiding has increasingly attracted scholars' and practitioners' attention but few in the family business context. Hence, this research aims to investigate how and why the employees hide tacit knowledge in the small family business. The present study used the Self-determination theory (SDT) as the theoretical foundation to explain knowledge hiding behaviours from the motivational perspective. The single case study was conducted in China, as Chinese family business has distinctive cultural characteristics influencing knowledge hiding. Data were collected and analysed from 22 participants in a small Research and Development company through semi-structured interviews and thematic analysis. The findings revealed that skilled employees used various methods to hide knowledge, such as pretending not to know, using no time as an excuse, and hiding the core knowledge. The reasons for knowledge hiding primarily reflected the unfair issues between the family and non-family employees in terms of the favouritism of the owner-manager toward the family employees, no bonus and ‘996’ timetable (people need to work from 9:00 am to 9:00 pm and 6 days per week) for the non-family members. Theoretically, this study contributes to understanding knowledge hiding behaviours by analysing motivations within SDT and corporate contextual influences in the small family business. These findings facilitate enhancing the owner-manager's awareness of the effects of unfairness on knowledge hiding and providing practical solutions to the unfairness and knowledge hiding among employees, as this has immense implications in any business.