This study aimed to evaluate the application of synbiotic containing multispecies of probiotics with different cell densities in white shrimp rearing against infectious myonecrosis virus (IMNV) and Vibrio parahaemolyticus coinfection. This study used a completely randomized design with five treatments and three replications. One additional replication of each treatment was provided for the lethal sampling. Pacific white shrimp were fed with three dosages of synbiotic multispecies for 30 days, namely 10 3 CFU mL −1 (Sin 3), 10 6 CFU mL −1 (Sin 6), and 10 9 CFU mL −1 (Sin 9), and the controls without synbiotic administration consisted of the positive control (K +) and the negative control (K −). Pacific white shrimp from all treatments, except for the K − , were challenged with IMNV a dose of 100 µL and 10 6 CFU mL −1 V . parahaemolyticus, injected intramuscularly. Infected Pacific white shrimp showed clinical signs like anorexia, melanosis, empty gut, colorless hepatopancreas, and white necrotic areas in striated skeletal muscles, especially of the distal abdominal segments and uropod. The results showed that administration of synbiotic for 30 days resulted in higher immune parameters, such as total hemocyte count (THC), phenoloxidase activity (PO), respiratory bursts (RB), and total viable bacterial count (TBC) compared to K + /K − . After coinfection, they showed significantly higher levels for THC, PO, RB, gene expression prophenoloxidase (ProPO), and lipopolysaccharide and β-1.3-glucan-binding protein (LGBP), better clinical signs, and lower mortalities. Sin 9 treatment significantly showed the highest survival rate (SR) compared to the other treatments.