A tetra-ester (TE) functionalized organic compound was synthesized for the restoration the mechanical properties of the PVC/Mg(OH) ₂ nanocomposites. The organically modified Mg(OH) ₂ nanoparticles (OMN) were prepared by surface modification of Mg(OH) ₂ nanoparticles (MDH) using a methylated tetra-phenol (TP) organic compound to achieve the homogeneous MDH distribution in the nanocomposite matrix. The results of FT-IR, XRD, and FE-SEM revealed the successful surface treating of MDH. The PVC nanocomposites were prepared by solvent blending and casting method. From the TGA analyses, the 10% mass loss temperature and the char yield of PVC containing 3% by mass of OMN and 3% by mass of TE, in N ₂ atmosphere, increased by 13 °C and 7%, respectively, compared to unfilled PVC. From the microscale combustion calorimeter, a decreasing heat release rate from 125.2 to 92.8 W g ^–1 was observed for PVC film filled with 6% by mass of each additive, compared to unfilled PVC. The tensile test results revealed that TE and OMN have been effective for the improvement of the PVC tensile strength. For example, incorporating only 6% by mass of each filler led to an improvement in tensile strength from 58.99 to 80.58 MPa, compared to unfilled PVC.