The sinterability and microwave dielectric properties of (Zr0.8Sn0.2)TiO4 with additions of 1 mol% of magnesium, calcium, strontium, or barium were examined, All the alkaline-earth metals were effective for densification, and the order of effectiveness was as follows: Mg < Ca < Sr < Ba, The dielectric constant and the temperature coefficient of the resonant frequency were not influenced very much by the additives; however, a strong deterioration of the quality factor (Q) did occur when magnesium was added. The presence of grain-boundary phases was confirmed via microstructural observation, using transmission electron microscopy, In addition, energy-dispersive X-ray analysis was performed to investigate the cause of the deterioration in the Q value.