The main objective of this work to explore new safe antiviral agents against hepatitis A virus (HAV), norovirus (NoV) and Coxsackievirus B4 (CoxB4) infections. In this context, we have successfully prepared new polyquaternary phosphonium oligochitosans (PQPOC) to use them as natural synergistic in-situ bioreductants of silver ions into nanosilver and stabilizing agent for these nanosilver to fabricate PQPOCs-AgNPs nano-biocomposites (NBC1,2). The antiviral performance of the PQPOCs and NBCs against FCV, HAV, and CoxB4 reflects great virucidal activities for NBCs as compared with PQPOCs with maximum viral reduction% (41.42, 80.62, and 84.04%) for NBC1 against FCV, HAV, and CoxB4, respectively. Furthermore, the antiviral activity of NBC1 is concentration- / pH-dependent where NBC1 acquired its maximum antiviral at [NBC1] = 200 μL/mL and pH 4. Based upon these facts, we could attribute the enhanced virucidal efficacy of NBC1: (i) binding of AgNPs to the virions active sites. (ii) Electrostatic interaction between the positive brushes of PQPOC and negative targets of viruses. (iii) Inducing ribonuclease catalyzed by CS to degrade the viral RNA and consequently prevents its transcription and translation.