Objective: Isolation, serological and molecular identification and differentiation between velogenic and lentogenic of Newcastle disease virus (NDV) strains.
Design: Descriptive study.
Procedures: In this study, A total of 24 Pooled samples  were collected from Dakahlia, Egypt, from 2017 to 2018 .The virus was isolated in 10 days old (ECEs) and serologically identified in third egg passage allantoic fluid by Haemagglutination (HA), Haemagglutination inhibition test (HIT) and agar gel precipitation test (AGPT). Molecular confirmation was done by reverse transcriptase-polymerase chain reaction (RT-PCR). Genetic diversity between velogenic and lentogenic NDV strains was done by RT-PCR amplification of 254bp F gene fragment from velogenic NDVs  and sequence analysis of 362bp NDV F gene fragment. 
Results: Out of 24 tested samples, 20 samples were collected from allontoic fluid of 3^rd passage positive by HA test, 18 samples by HIT, 16 samples by AGPT and 18 isolates were positive with RT-PCR amplification of 362bp F gene fragment. LaSota strain gave positive results in HA, HIT, AGPT and RT-PCR amplification of 362bp fragment. Interestingly, 254bp fragment failed to be amplified from LaSota strain. The phylogenic analysis revealed that our isolates were related to Egyptian velogenic genotype VII NDVs. The deduced amino acid sequence of the F protein cleavage site of our isolates was characteristic of velogenic NDVs (¹¹²R-R-Q-K-R^↓F¹¹⁷) while LaSota strain had characteristic lentogenic NDVs cleavage site (¹¹²G-R-Q-G-R^↓L¹¹⁷).
Conclusion and clinical relevance: RT-PCR and sequence analysis in this study can be used for differentiation between velogenic and lentogenic NDV strains.