Abstrak Telah dibuat kaca dengan komposisi (70-x) P2O5 – 30 MgO – x ZnO dengan variasi konsentrasi ZnO dari 0 sampai 15 mol% menggunakan teknik melt-quenching. Sampel yang dibuat memiliki komposisi MgO tetap yaitu 30 mol%. Sifat termal dan struktur kaca diteliti dengan  differential thermal analysis (DTA),X-Ray Diffraction (XRD),  and Fourier-transformed infrared (FTIR). Hasil XRD menunjukan bahwa kaca merupakan amorf. Didapatkan nilai stabilitas termal (∆T) meningkat seiring dengan penambahan ZnO sampai 10 mol% kemudian menurun dengan penambahan mol %ZnO. Komposisi 5mol% dari ZnO memiliki nilai ∆T dan Hurby (H) tertinggi yang artinya paling stabil diantara seluruh sampel. Sedangkan, hasil FTIR menyatakan bahwa bilangan gelombang dari P-O-P meingkat dan P=O berkurang dengan penambahan ZnO. Dari informasi ini didapatkan nilai BO meningkat dan NBO berkurang seiring dengan peningkatan ZnO. Kata-kata kunci: Kaca Fosfat, Melt-Quenching, Sifat Termal, Struktur Fosfat Abstract (70-x) P2O5 – 30 MgO – x ZnO glasses containing different concentrations of ZnO ranging from 0 to 15 mol% were prepared by the melt-quenching technique. The sample had a fixed MgO content of 30%. The thermal and structural properties of these glasses were investigated by means of differential thermal analysis (DTA),X-Ray Diffraction (XRD),  and Fourier-transformed infrared (FTIR). Result from XRD show that the glass are amorphous. It has been found that the thermal stability (∆T) increase as ZnO is added into the glass sample and decrease afterward. Composition of 5 % ZnO possesses the highest value of  ∆T and Hurby’s value (H) of all samples which mean that the sample is the most stable. Meanwhile, FTIR test demonstrate that the wavenumber of P-O-P increase and P=O reduces as the ZnO content increase. From this information, the number of BO increase and NBO decrease as the ZnO content increase.  Keywords: Phosphate glasses, Melt-Quenching, Thermal Properties, Phosphate Structure