Perkembangan nanokomposit berasaskan polimer dan pengisi bersaiz nano telah menjadi pendekatan yang menarik untuk mencapai sifat komposit yang baik. Kesan nano–termendak kalsium karbonat (NPCC) terhadap sifat mekanikal matrik berlainan kemuluran telah dikaji. Poli(vinil klorida) tanpa pemplastik (PVC–U) dan PVC–U/akrilik telah digunakan sebagai matrik pada kajian ini. Untuk menghasilkan komposit, resin PVC, additif, akrilik dan NPCC pada mulanya diadun-kering menggunakan pencampur berkelajuan–tinggi berskala makmal sebelum diadun menjadi kepingan dengan menggunakan pengadun dua pengguling. Spesimen–spesimen ujian kemudiannya ditekan panas, selepas itu sifat mekanikal komposit dan morfologi permukaan patah komposit ditentukan. Modulus lenturan dan modulus Young meningkat dengan penambahan NPCC, tetapi telah menurunkan kekuatan regangan. NPCC telah menunjukkan kesan pengukuhan yang baik pada matrik PVC–U/ akrilik dan kesan kekakuan yang baik pada matrik PVC–U. Kekuatan lenturan kedua–dua komposit tidak dipengaruhi dengan penambahan NPCC. Kekuatan hentaman kedua–dua komposit telah mencapai nilai maksimum apabila 15 phr NPCC ditambah. Kata kunci: Poli(vinil klorida), nano–termendak kalsium karbonat, sifat–sifat mekanikal, akrilik Developing nanocomposites based upon polymers and nano–sized fillers has been an attractive approach to achieving good properties. Effects of nano–precipitated calcium carbonate (NPCC) on the mechanical properties of different ductile matrices were investigated. Unplasticised Poly(vinyl chloride) (PVC–U) and PVC–U/acrylic were used as the matrix in this study. To produce the composites, PVC resins, additives, acrylic and NPCC were first dry–blended using a laboratory high–speed mixer before being milled into sheets on a two–roll mill. Test specimens were then hot pressed, after that the mechanical properties and morphology of fracture surface of composites were determined. The flexural modulus and Young modulus of both the composites were enhanced after the addition of NPCC, but the tensile strength was decreased. The NPCC showed good toughening effect and stiffening effect on PVC–U/acrylic and PVC–U matrix, respectively. The flexural strength of both the composites was not significantly affected by the addition of NPCC. The impact strength of both the composites reached the maximum value when 15 phr NPCC was incorporated. Key words: Poly(vinyl chloride), nano–precipitated calcium carbonate, mechanical properties, acrylic