Pendahuluan: Nilon termoplastik adalah material basis gigi tiruan yang terbuat dari resin poliamida yang perlu dibersihkan secara berkala. Cuka sari apel dan Val-clean digunakan sebagai bahan pembersih gigi tiruan, namun bahan tersebut dapat mempengaruhi sifat fisis dan mekanis seperti stabilitas warna dan kekuatan fleksural. Tujuan penelitian menganalisis pengaruh perendaman cuka sari apel konsentrasi 5% terhadap stabilitas warna dan kekuatan fleksural basis gigi tiruan nilon termoplastik. Metode: Jenis penelitian eksperimental laboratoris dengan post-test-only control group design. Jumlah sampel terdiri dari 48 dengan ukuran sampel 20x3 mm untuk uji stabilitas warna dan 65x10x3±0,1 mm untuk uji kekuatan fleksural dan terbagi menjadi enam kelompok sampel. Stabilitas warna diukur menggunakan colorimeter dan kekuatan fleksural menggunakan Universal Testing Machine. Analisis data menggunakan uji ANOVA. Hasil: Stabilitas warna menunjukkan tidak ada pengaruh signifikan p=0,124 (p>0,05) antara kelompok perendaman cuka sari apel konsentrasi 5%, Val-clean, dan akuades selama 4 hari, sedangkan kelompok perendaman cuka sari apel konsentrasi 5%, Val-clean, dan akuades selama 8 hari menunjukkan ada pengaruh yang signifikan p=0,035 (p<0,05). Uji ANOVA terhadap kekuatan fleksural menunjukkan ada pengaruh yang signifikan p=0,001 (p<0,05) antara kelompok perendaman cuka sari apel konsentrasi 5%, Val-clean, dan akuades selama 4 hari dan 8 hari. Simpulan: Perendaman cuka sari apel tidak disarankan untuk bahan pembersih basis gigi tiruan nilon termoplastik karena dapat menyebabkan perubahan warna dan dapat menurunkan kekuatan fleksural.Kata kunci: nilon termoplastik; cuka apel 5%; stabilitas warna; kekuatan fleksural ABSTRACT Introduction: Thermoplastic nylon is a denture base material made of polyamide resin that needs to be cleaned regu-larly. Apple cider vinegar and Val-clean are used as denture cleaning agents, but they can affect physical and mechanical properties such as colour stability and flexural strength. The purpose of this study was to analyse the effect of immersion in 5% of apple cider vinegar on the colour stability and flexural strength of thermoplastic nylon denture bases. Methods: This research was an experimental laboratory with a post-test-only control group design. Forty-eight samples were fabricated with the size of 20x3 mm for colour stability test and 65x10x3±0.1 mm for flexural strength test, then divided into six sample groups. Colour stability was measured using a colourimeter and flexural strength using a Universal Testing Machine. Data analysis was performed with an ANOVA test. Results: After four days of immersion, colour stability showed no significant effect (p=0.124; p>0.05) between the 5% apple cider vinegar immersion group, Val-clean, and distilled water. While after eight days of immersion, the 5% apple cider vinegar immersion group, Val-clean, and distilled water showed a significant effect (p=0.035; p<0.05). ANOVA test on flexural strength showed a significant effect (p=0.001; p<0.05) between groups of 5% apple cider vinegar immersion, Val-clean, and distilled water after four and eight days of immersion. Conclusions: Thermoplastic nylon denture base is not recommended to be immersed in apple cider vinegar for cleaning because it can cause discolouration and reduce flexural strength.Keywords: thermoplastic nylon; 5% apple cider vinegar; colour stability; flexural strength