Temperature dependences of dielectric, ferroelectric, elastic, piezoelectric, and optical properties of a new ferroelectric crystal, SrTeO3, have been measured. Ferroelectricity in this crystal is confined to the temperature range between 312 and 485°C. All the measured constants exhibit abrupt changes at 312°C, which shows the phase transition at this temperature to be of the first order. The electromechanical coupling factorsk21andk22at 312°C are 0.34 and 0.37, respectively, which are large in spite of the small value of the spontaneous polarization; 0.037 C/m2. The temperature dependence of the piezoelectric constantd22is well explained by the dielectric constant and the spontaneous polarization, while that ofd21seems to be peculiar; i.e., it monotonically decreases to nearly zero at the upper transition point. The elastic compliancesS11DandS22Dshow no anomaly in the ferroelectric temperature range. The obtained value of 17.3 eV for the dispersion energy of the refractive indexnbindicates that this crystal may be built up by the tetrahedral framework. Phase‐transition temperatures in the solid‐solution systems Sr1−xBaxTeO3and Sr1−xCaxTeO3are studied on ceramic samples. The two transition points decrease with increasingxin both systems.