Study on the correlation between water quality and microbiology to cultured clam (Meretrix lyrata) was carried out in Ben Tre province and Can Gio district Ho Chi Minh city. The study was conducted in the period of time from November 2009 to November 2010 in Ben Tre province and from October 2009 to October 2010 in Can Gio district Ho Chi Minh city. Temperature, pH, sanility, alkalinity, NH4
-N and NO2-
N were sampled in the culture area every day. Water and sediment sample were taked in situation of disease occur to define the total of Vibrio in samples. The results showed that in Ben Tre province, the average value of pH, temperature and salinity in investigating period was 8, 30.2 + or - 1.49°C and 27.7 + or - 6.34 percent), respectively. This results demonstrated that water quality and cultured clam health were not correlated, but the salinity and apperance of Vibrio were high resulting to cultured clam health in Ben Tre province. In Can Gio district - Ho Chi Minh city, the average value of temperature and salinity in investigating period was 28.1 + or - 1.4°C and 20.1 + or - 4.9 percent), respectively. This results presented that the salinity affected to cultured clam, especially, in status of droping salinity and high density fungi in water which affect to cultured clam.