The haematology laboratory at Hospital Universiti Sains Malaysia implements sample acceptance and rejection according to the rejection criteria following guidelines by ISO 15189. This study aims to evaluate causes and types of samples rejection and we also introduce an initiative to reduce sample rejection. A 2- month retrospective study was conducted by obtaining and evaluating data from samples sent to the haematology laboratory from June and July 2022. The laboratory received a total of 32,726 samples, out of which 1,084 (3.31%) were rejected. Rejection rates were 3.19% and 3.43% consecutively for June and July 2022. The leading cause of sample rejection was clotted samples (36.6%), followed by duplicate requests (22.9%), and insufficient amounts (16.9%). High sample rejection rates were recorded from the paediatric surgical ward, medical high-dependency unit, and otorhinolaryngology ward. The lowest rejection rate was from the outpatient clinic. The overall sample rejection rate was 3%. Therefore, a few mitigation strategies need to be employed to improve the acceptance rate.