The sediment transport characteristics and historical trends of total sediment supply of the Chao Phraya River, which is the major sediment supply source to the Upper Gulf of Thailand, has been evaluated based on hydrographic surveys of the Chao Phraya River during the period 2012–2013. Detailed analyses of river characteristics conducted in this study combined with historical data indicate that suspended transport rates at the Chao Phraya River have a strong correlation with river discharge, and the relationship can be represented by a power equation with a coefficient of determination of 0.80. It also appears that this bed-to suspended load ratio varied in a narrow range between 0 and 0.05. A time series evaluation of total sediment load over 58-years period indicates that a significant reduction in the total sediment yield of the CPY River occurred after 1995, and it may cause by water management in the CPY River basin but significantly post-dates of the construction of large dams in this basin.