This study was carried out to evaluate water quality, key water parameters and frequency of surface water monitoring in the upper part of Hau river in Vietnamese Mekong Delta using statistical approaches. The water quality data was collected at two locations including MH1 (upstream water entering Hau River in An Giang province) and MH2 (water in Hau river leaving An Giang province. Water quality data were collected in 2020 from January to November with a frequency of 4 times per month. Nine water quality parameters comprising temperature, pH, dissolved oxygen (DO), suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD), nitrate (N-NO3-), orthophosphate (P-PO43-) and coliform were used evaluate surface water quality. The national standard on surface water quality (QCVN 08-MT:2015/BTNMT, column A1, cluster analysis (CA) and Principal Component Analysis (PCA) were used to evaluate water quality, sampling frequency and key parameters influencing surface water quality in the study area. The results showed that surface water in Hau river belonging to An Giang province was polluted by DO, TSS, COD, BOD, P-PO43- and coliform. June and August were the months with the highest level of water pollution. The water quality in the study area tended to be low in the dry season (March to June), but high in the rainy season (July to October). CA cluster reduced the sampling frequencies from 11 to 4, saving cost of monitoring by 63.63%. The PCA results showed that three potential sources which could explain 75.5% of the variation in water quality. Nine water parameters all caused affecting the changes of water quality. The study contributes to providing important information on surface water quality for the process of monitoring and planning water use for domestic purposes and conservation in Hau river area, An Giang province.