Serological assays can be used for evaluating immune response post vaccination, they can be also helpful in studying the status of maternally derived antibodies (MDA), and they can also give a diagnostic mirror for viral sero-epidemiology. In the present study comparison between hemagglutination inhibition test (HI) and Enzyme linked immunesorbant assay (ELISA) and their abilities to detect IBV antibodies at different circumstances (post vaccination, infection, and (MDA) was studied. HI test for IBV was performed against two distinct IBV serotypes namely (Mass- 41, 4/91). Since they are the major vaccines used commercially in the Egyptian market. ELISA was performed at two dilutions (1/100, 1/ 1000) which is nearly the reciprocal of dilution of (7 and 10) in HI test in a trial to set two points for comparing the obtained results From the two tests. ELISA test showed 100% sensitivity and specificity at dilution 1/100 and showed 80.96%, 95.5 % respectively at 1/1000 dilution. The sensitivity and specificity of HI test were 80.91%, 95% respectively when Mass-41 antigen was used and was 73.91 %, 62 % when 4/91 antigen was used .The difference in sensitivity and specificity with HI reflects it selectivity during serotyping and this picture will necessarily differ if samples were tested against other antigens like (D- 274, 1466,…..etc.,) this confirms our point of view for using HI in detecting immunity after IBV vaccination. It became obvious that ELISA result may be misleading as seen during studying MDA in sample (S-20), ELISA reading at 1/100 dilution was 12051±2018 with STDV(6384) and was 2406±754 with STDV(2385) at dilution 1/1000 their Conversion into two base log titer 1/10 will be 14.28±.317 and 14.56±.4 respectively on the other hand the HI titer was 4.5±.166 with STDV(0.5) when Mass – 41 antigen was used and it was 2.4±.476 with STDV (1.5) when antigen 4/91 was used, result of ELISA will be conflicting when devising a vaccination protocol for such flock.