While many studies have attempted to understand knowledge-sharing practices in the health-care industry, there is a dearth of knowledge about the determinants of the knowledge-sharing behaviour of pharmacists. The present study employed theory of planned behaviour constructs and personality traits to assess factors affecting the knowledge-sharing behaviour of pharmacists in Oyo State, Nigeria. A descriptive survey research design was adopted, with the use of a structured questionnaire as the data collection instrument. Relevant descriptive and inferential statistical analyses were carried out on the collected data. The findings revealed that there is a positive relationship between attitude, subjective norms, perceived behavioural control, openness to experience, agreeableness and knowledge-sharing behaviour. This implies that pharmacists whose personality traits tend towards openness to experience and agreeableness will share their knowledge more readily than those whose personality traits do not. Also, pharmacists’ knowledge-sharing behaviour can be enhanced through improvements in their attitude towards knowledge sharing, subjective norms and their perceived behavioural control.