Based on recent 52 years (1962-2013) daily precipitation data of 86 weather stations in Guangdong, the annual rainy season onset dates (RSOD) of each station were counted, and the characteristics of the rainy season onset and its relationship with the first rainy season precipitation were analyzed. The results indicate that: (1) The RSOD is mainly concentrated in the last dekad of March to the mid dekad of April, and there is a 94 d gap between the earliest and the latest dates; (2) The rainy season begins earlier in southeast and north of Guangdong than in the southwestern part, and the latest in Leizhou Peninsula; (3) The rainy season begins in the two types of abrupt onset and gradual onset; (4) The RSOD has an inter decadal oscillation period of 15-16 years, and respective inter annual oscillation period of 8 years and 5-6 years pre and post 1986; (5) The RSOD has good correlations with late March and April precipitation but is poor with precipitation in May, June and the first rainy season; (6) The 500 hPa circulation differs greatly between the RSOD earlier years and the later years.