Salah satu tahap dalam fertilisasi in vitro (FIV) adalah seleksi inti oosit matur yang akan digunakandalam fertilisasi. Inti oosit yang matur tersebut ditandai dengan adanya polar body di dalamnya.Cara yang sederhana dan praktis dalam menentukan maturitas inti oosit adalah pengukuran diameterfolikel. Terdapat perbedaan pendapat mengenai diameter folikel yang berhubungan terhadap maturitasinti oosit.Penelitian ini bertujuan untuk mengetahuihubungan antara diameterfolikeldenganmaturitasintioositpada program FIV.Rancangan penelitian ini observasional analitik(cross-sectional) yang dilaksanakan di Klinik Bayi Tabung Graha Tunjung, RSUP Sanglah, Denpasar.Sampel penelitian adalah folikel-folikel yang mengandung inti oosit (61 folikel), dilakukan dengancara consecutive sampling mulai 1 September 2011-31 Agustus 2012. Data dianalisismemakai ujiFisher Exact. Sebanyak 61 sampel diukur diameternya dengan menggunakan transvaginalsonography.Didapatkansebanyak 33folikeldengan diameter > 18 mm denganperincian 32mengandungoositmatur (96,97%) dan1 mengandungoositimatur (3,03%), sedangkandari 28folikeldengan diameter < 18 mm, didapatkansebanyak 21 folikelyang mengandungoositmatur (75%)dan 7 folikel yang mengandung oositi matur (30%). Hasil penelitian menunjukkan bahwa terdapathubungan antara diameter folikeldengan maturitas inti oosit pada siklus antagonis FIV secarabermakna (x2=4,63; P=0,019). Disimpulkan bahwa terdapat hubungan antara diameter folikel denganmaturitas inti oosit pada siklus antagonis FIV. [MEDICINA 2015;46:12-15].One of the stages in in vitro fertilization (IVF) is the selection of mature oocyte nucleus. This matureoocyte nucleus is characterized by the presence of polar body inside. Simple and practical way todetermine the maturity of the oocytenucleus is the measurement of follicle?s diameter. There aredifferences of opinion on the follicle?s diameter associated with the maturity of the oocyte nucleus. Thisstudy is purposed to know the relationship between follicle?s diameter with oocyte nucleus maturity inantagonist cycle IVF. This study?s design is observational analytic study (cross-sectional). This studywas done at Graha Tunjung IVF Clinic, Sanglah Hospital. Sample from this study were follicles thathave oocyte nucleus (61 follicles). Samples were collected with consecutive sampling from September1st 2011?August 31st 2012. Datas were analyzed with Fisher Exact test. As many as 61 samplesmeasure follicle?s diameter was count by transvaginal sonography.We analyzed 34 follicles withdiameter > 18 mm which is consist of 32 mature oocytes (96.97%) and 1 immature oocyte (3.03%), thenfrom 28 follicles with diameter < 18 mm, we found 21 follicles withmature oocyte (75%) and 7 follicleswith immature oocyte (30%).This study?s design shows relationship between follicle?s diameter andoocyte nucleus maturation in antagonist cycle IVF significantly (x2=4.63; P=0.019). It is concluded thatthere is a relationship between follicle?s diameter with oocyte nucleus maturity in antagonist cycleIVF. [MEDICINA 2015;46:12-15].