ABSTRAK Telah dilakukan penelitian pengaruh pati biji durian (Durio zibethinus) sebagai bahan pengisi terhadap kuat tarik dan biodegradasi komposit polimer polistirena (PS). Pada penelitian ini dibuat sampel dengan 5 variasi komposisi Polistirena : Pati : Gliserol yaitu 95:0:5 ; 90:5:5 ; 85:10:5 ; 80:15:5 dan 75:20:5 %. Sampel dicetak menggunakan hotpress sesuai ASTM D368. Kemudian dilakukan pengujian sifat mekanik (kuat tarik) dengan menggunakan alat uji tarik, pengujian gugus fungsi menggunakan FT-IR, morfologi permukaan menggunakan AFM dan biodegradasi melalui penguburan selama 40 hari (waktu pengamatan 1, 2, 3, 4 dan 5 minggu). Hasil penelitian menunjukkan bahwa nilai kuat tarik dipengaruhi oleh variasi komposisi bahan baku komposit dengan nilai kuat tarik optimum didapatkan pada sampel PS-2 (90% PS : 5% pati : 5% gliserol) dengan nilai kuat tarik 0,55 kgf/mm². Berdasarkan analisa gugus fungsi diketahui bahwa tidak terbentuk senyawa baru, yang ditandai dengan tidak munculnya gugus fungsi baru pada sampel komposit. Hasil analisa morfologi permukaan menunjukkan bahwa variasi komposisi relatif tidak mempengaruhi morfologi permukaan sampel komposit. Dan hasil uji biodegradasi menunjukkan bahwa pada sampel PS-4 dan PS-5 mulai terdegradasi setelah penguburan selama 4 minggu. Kata kunci: Polistirena, Pati Biji Durian, Kuat Tarik, Gugus Fungsi, Morfologi Permukaan dan Biodegradasi. ABSTRACT The study of starch seeds durian (Durio zibethinus) effect as the filler material on tensile strength and biodegradation of polymers polystyrene (PS) has been done. In this study, the sample was made with 5 variations Polystyrene : Starch : glycerol made as 95:0:5; 90:5:5; 85:10:5; 80:15:5 and 75:20:5 %. The samples were printed using the hotpress machine and followed the ASTM D368 standard. Then the mechanical properties (tensile strength) test of the sample using a tensile tester, the testing for functional groups using FT-IR, furthermore the surface morphology obtained by AFM and biodegradation through burial the samples for 40 days (time of observation 1, 2, 3, 4 and 5 weeks). As the results, showed that the tensile strength values are influenced by variations in the composition of composite materials with optimum tensile strength values obtained on samples of PS-2 (90% PS: 5% Starch: 5% glycerol) with a tensile strength value of 0.55 kgf / mm ², but have not found a better tensile strength than previous research. Based on the analysis of functional groups, it was found that there is no chemical reaction, which is characterized by the emergence of new functional groups on the composite sample. The surface morphology observation showed that the variation does not affect the relative composition of the surface morphology of the samples. And biodegradation test results showed that the samples of PS-4 and PS-5 began degraded after burial for 4 weeks. Keywords: Polystyrene, Starch Seeds Durian, Tensile Strength, Functional Groups, Surface Morphology and Biodegradation.