This paper studied the determinants of workplace deviant behaviours (WDB) among non-academic staff in universities in South-South Nigeria. Three hundred (300) non-academic staff were drawn equally from the six universities in the six states that make up the South-South region of Nigeria. Data were generated from two hundred and nineteen (219) questionnaires received from the respondents without errors and analyzed using Pearson's Product Moment Correlation. The results found that vandalism, manipulation of records, abuse of office, wastage of office resources, leaving early from work, favouritism, gossiping, and aggression towards colleagues were prominently workplace deviant behaviour. In addition, the study established that the individual-related factors that cause these deviant behaviours are job stress, personality traits, emotional intelligence and moral deviation, while interpersonal factors are group norms and group behaviours. In the same vein, the organizational factors include workplace religiousity, workplace support, job security, career management, and HR practices. The study concludes that a statistically significant relationship exists between the two major categories of workplace deviant behaviours, interpersonal and organizational factors responsible for deviant behaviours practiced among non-academic staff in universities in South-South Nigeria. The study recommends that university management should set up a committee to strictly address and combat the identified deviant behaviours that are commonly practiced among her non-academic staff in the institution.