This study investigates DL practice among heads of library and job performance of librarians in HEIs in Nigeria. A descriptive design of survey type was applied for the study. The 164 librarians (19 heads of library and 145 librarians) in 19 public higher educational institutions (HEIs) in Ekiti, Ondo and Osun States formed the population of the study. The study adopted total enumeration sampling technique. A self-structured close-ended questionnaire and interview were used for data collection. It was found that the levels of DL among the heads of library and job performance among librarians in HEIs in Nigeria are high. The study also found that there is significant relationship between: delegation of duties and job performance, delegated decision making and staff job performance, delegated instructional supervision and job performance, and delegated administrative supervision and job performance among the librarians. There is no significant difference between the levels of DL among the male and female heads of the library. It was recommended that subordinate librarians should be trained to develop their leadership capacity to perform optimally when leadership role is distributed to them within the library.