The formation and variation in intensity of summer monsoon is one most important aspect of monsoon problems. Investigation is undertaken on the East Asian monsoon indices in the context of 1951～1992 sea level pressure (SLP) and Pacific sea surface temperature (SST) data, trying to discuss the relationship between summer monsoon and ENSO. It is shown that the East Asian summer monsoon is weaker in the mature year of El Nino as composed to that of La Nina, but V.V. for their next year.