The present work was conducted to determine the occurrence of streptococcal infection in the disease outbreak (summer mortality syndrome) affecting Nile tilapia farms located at Kafrelsheikh Provence, northern Egypt. Affected farms were suffered from increased mortalities with appearance of different classical signs indicating bacterial infection. One hundred and forty clinically diseased fish samples were collected from seven diseased farms. Initial bacterial isolation on modified Edwards's medium indicated the presence of 30 Streptococcus isolates, half of them was further identified by polymerase chain reaction as S. iniae. Molecular study revealed the presence of six virulence associated genes in the recovered S. iniae isolates. The recovered genes are scpl, simA, pdi, SagA, pgmA and cpsD, these genes were detected in 7, 7, 5, 4, 3 and 9 isolates representing 46.6, 46.6, 33.3, 26.6, 20 and 60% respectively. Virulence associated genes may have a potential role in disease severity and promoting the pathogenicity of bacterial infection.