Abstract: Background: Error in any laboratory starts from the moment any investigation is being planned till it is interpreted and clinical judgment is made. Entire process is difficult to perform without error. Aim : Study of the Errors in hematology laboratory in a tertiary care hospital. TeerthankerMahaveer Medical college and Research center (Moradabad). Purpose: To investigate for errors and causes of errors related to different hematological tests in hematology laboratory. Methodology: In this observational study, a total of 304,358 tests (95,991 outpatient department [OPD] and 208,367 inpatient department [IPD]) were received in haematology laboratory. These errors were further categorized as Pre-analytical, Analytical and Postanalytical. Result: The Pre-analytical errors constituted maximum number of errors i.e.in 501samples (94.7% of total errors) which constituted major chunk of errors which is close to 0.16%, which was followed by post analytical errors which was found in 17cases (3.21% of total errors) with frequency of 0.0036% ;Analytical errors were detected in least number of cases i.e.11reports (2.07% of total errors) Conclusion: Errors in hematology laboratory which is classified as Pre-analytical, analytical, and post-analytical errors remain the biggest limitation to laboratory service and it thus has impact on healthcare management and cost involved. Majority of reasons involved behind analytical errors is within the scope of laboratory and thus can be reduced to a great extent by training of laboratory staff, participation in quality system and regular monitoring of equipment’s. We found analytical error to be close to 2% most of which were related to auto clumps which can be resolved by incubation at body temperature most of the time as these are cold auto agglutinins which poses analytical problem, especially in winters. We found Post analytical error also to be insignificant (3.2%), most of which was due to wrong entry of results, such errors can also be avoided and minimized by close and frequent monitoring of laboratory reports.