Pendahuluan: Resin akrilik heat cured (HC) merupakan pilihan utama bahan sebagai basis gigi tiruan. Hidroksiapatit (HAP) adalah molekul kristalin yang sudah banyak digunakan di kedokteran gigi. Penelitian terdahulu membuktikan bahwa HAP mampu mengurangi monomer sisa pada resin akrilik HC, yang akan mengurangi juga porositas resin akrilik tersebut. Berkurangnya porositas resin akrilik, diharapkan akan meningkatkan kekuatan mekanik resin akrilik tersebut. Tujuan penelitian menganalisis pengaruh penambahan hidroksiapatit terhadap porositas dan compressive strength resin akrilik HC. Metode: Jenis penelitian eksperimental laboratoris. Sampel penelitian 20 resin akrilik HC berbentuk silindris (6x3mm), dibagi menjadi 4 kelompok. Kelompok kontrol (tanpa penambahan HAP), kelompok HAP 2%, kelompok HAP 5%, dan kelompok HAP 10%. Permukaan sampel diteliti menggunakan SEM untuk porositasnya. Penghitungan compressive strength sampel menggunakan Universal Testing Machine (load cell 300kg/mm2). Hasil: Uji one-way ANOVA dan Tukey-HSD menunjukkan perbedaan signifikan (p<0,05) antara kelompok kontrol (90±13,5MPa) dengan 5%HAP (105±4,3MPa) dan 10%HAP (113±10,2MPa), begitu pula antara 2%HAP (96±8,4MPa) dengan 10%HAP. Uji SEM menunjukkan tidak adanya reaksi kimia antara HAP dan resin akrilik HC. Tampak pula bercak putih tersebar tidak merata pada permukaan sampel akrilik di kelompok-kelompok perlakuan. Bercak putih ditemukan meningkat sebanding dengan peningkatan konsentrasi HAP, dengan diameter yang semakin besar. Simpulan: Penambahan HAP pada basis resin akrilik HC mampu menurunkan tingkat porositas dan meningkatkan nilai compressive strength. Penurunan tingkat porositas meningkat seiring dengan penambahan HAP. Compressive strength yang paling tinggi didapatkan pada basis resin akrilik heat cured dengan penambahan 10% hidroksiapatit. Kata kunci: Compressive strength, uji SEM, resin akrilik heat cured, hidroksiapatit.   ABSTRACT Introduction: Heat-cured acrylic resin has been commonly used as a denture base, whereas hydroxyapatite (HAP) is a crystalline molecule widely used in the field of dentistry. Previous research has been proofed that HAP could reduce the residual monomer of heat-cured acrylic resin, which will reduce the porosity level in advance, so it was expected for better mechanical properties. This research was aimed to analyse the effect of HAP addition towards the porosity level and compressive strength of heat-cured acrylic resin. Methods: An experimental laboratory research was conducted towards 20 cylindrical samples (6 x 3 mm) of heat-cured acrylic resins, which were divided into four groups: Control group (without HAP addition), 2% HAP addition group, 5% HAP addition group, and 10% HAP addition group. Compressive strength was tested using Universal Testing Machine (load cell of 300kg / mm2). Each sample surface porosity was observed using the scanning electron microscope (SEM). Results: One-way ANOVA and Tukey-HSD tests results showed significant differences (p < 0.05) between compressive strength in the control group (90 ± 13.5 MPa) compared to 5% (105 ± 4.3 MPa) and 10% HAP addition group (113 ± 10.2 MPa), significant differences were also shown between the 2% (96±8.4MPa) and 10% HAP addition group. SEM imaging showed that there was no chemical reaction between HAP and heat-cured acrylic resin. It showed uneven white spots in acrylic sample’s surface in all treatment groups. Those white spots were likely to be found more in the higher concentration of HAP, so did the diameter of white spots was also found more in the higher concentration. Conclusion: The addition of hydroxyapatite to the base of heat-cured acrylic resin can reduce the level of porosity and increase the compressive strength value. The decrease in the porosity level increases with the addition of hydroxyapatite. The highest compressive strength is obtained with the addition of 10% hydroxyapatite. Keywords: Compressive strength, SEM imaging, heat-cured acrylic resin, hydroxyapatite.