Upper Circumpolar Deep Water (UCDW) and North Pacific Deep Water (NPDW) coexist in the upper deep layer (i.e., with a 1.2-2.0-degrees C potential temperature range and a 2 000-4 100-dbar pressure range) of the Eastern Philippine Sea. They have similar properties in potential temperature and salinity, while have a significant difference in dissolved silicate. Based on the repeated observations along a 137 degrees E transect from the World Ocean Database (WOD18), this study revealed the interannual variability of dissolved silicate in the upper deep layer of the Eastern Philippine Sea. Dissolved silicate increased in 1995, 1996, 2005, 2006, and 2007, and decreased in 1997, 2000, 2001, 2002, and 2004. Composition analysis showed that the large difference between positive and negative dissolved silicate anomalies occurred mainly at similar to 15 degrees N and north of 25 degrees N, with the concentration reaching 4.25 mu mol/g. Further analysis indicated that the interannual dissolved silicate variability was related to the zonal current variation in the upper deep layer. The relatively strong (weak) westward current transport increased (decreased) NPDW to the Eastern Philippine Sea, thereby resulting in increased (decreased) dissolved silicate.