The Estimate of Runoff in Ping Watersheds of Northern Region of Thailand   Sathaporn Jaiarree   ABSTRACT         The estimate of runoff in Ping watershed of nothern region of Thailand in 1990 was done by collecting the annual runoff, annual rainfall and size area of the watershed which were recorded from the hydrological station of the Royal Irrigation Department (RID) and EGAT.       All data were collected stimunously for 10 years from 25 stations of RID and 20 stations of EGAT. For the result, the average annual rainfall in range from 920 to 1,490 mm. per year which was shown as the Isohyet map derived into 3 ares, 1) Upper part, 1,100 - 1,400 mm./yr 2) Middle and western part, 900 -1,100 mm./yr. 3) Lower part, 900 to 1,100 mm/yr.       The average annual runoff in range from 111 to 552 mm./yr.. Which was shown as the Isoline map. The correlation of runoff and rainfall was calculated as the correlation coefficient (r) is 0.810. And the average annual evapotranspiration is range from 626 to 938 mm./yr..Which was shown as the Isoline map compared with the annual rainfall and annual runoff in water balance equation. The estimate of runoff in Ping watershed can be calculated by using the statistical analysis in term of simple linear regression shown as the equation following ; Q = 0.869 P - 627, r = 0.810 when Q= Average annual runoff (mm.), P= Average annual rainfall (mm.) and R= Correlation coefficient.         Keywords : Runoff , Isohyet