Using NCEP/NCAR reanalysis data, the criterion for defining the date of the establishment process of the South Asia high (SAH) over the Indo-China Peninsula (ICP) was analyzed. The results indicate that the average commencement date is April 29th. The process begins with an anticyclonic circulation over the southeast of the Philippine Sea, which breaks into two; the western one moves westward and strengthens over the ICP owing to the diabatic heating over the ICP. Using the OLR provided by NOAA, the onset of the South Asian summer monsoon during the SAH development over the ICP was analyzed. The results show that the South Asian summer monsoon starts to build over the ICP at almost the same time as the establishment of the SAH over the ICP. After a few days of the commencement of the SAH development over the ICP, the summer monsoon over the east of the Bay of Bengal begins to develop. About 20 days later, it starts developing over the South China Sea and the Philippine Sea. Approximately one month later, it begins developing over the west of the Bay of Bengal, the Indian peninsula, and the east of the Arabian Sea. Thus, the establishment of the SAH over the ICP can be regarded as a good indicator of the onset of the South Asian summer.