In this study, ultra-thin poly(ether-block-amide, PEBA)-coated poly(vinyl alcohol, PVA) composite membranes were prepared and assessed for the removal of lead, zinc, lithium, arsenic, and copper from seawater. Effects of the coating numbers and temperature on flux and ion rejection were evaluated. The number of coating processes increased the thicknesses of the membranes. The ion rejection and water flux decreased with the increasing coating process. Dissolved ions were retained with a rejection of >99.5%. The highest rejections of 99.99% and 99.98% were obtained for sodium and magnesium ions. The coated PVA membranes showed a superior heavy-metal removal greater than 88%. The highest rejection improvements were obtained for zinc (Zn), lithium (Li), and copper (Cu) metals. The zinc, copper, and lithium rejections increased from 89.1%, 88.3%, and 85.1% to 95.3%, 98.46% and 94.4% due to the PEBA coating process, respectively. The influence of PVA thickness on the flux and rejection was also investigated. Increasing the thickness of PVA decreased the flux. The highest flux of 2.34 kg/m2.h was obtained with the membrane having a thickness of 90 µm.