Vertical and temporal variations of active and total bacterial abundance were monthly estimated in Lake Soyang from April 1999 to January 2000. The number of total and respiring bacteria was determined directly under microscope by AODC and CTC methods, respectively. The number of total and active bacteria varied from $2.1{ imes}10^5 to 3.1{ imes}10^6 $,$cells{cdot}ml^{-1}$ and $1.8{ imes}10^4 to 8.0{ imes}10^5 $,$cells{cdot}ml^{-1}$, respectively. The proportions of respiring bacteria to total cell ranged from 3.7 to 44.2% : The proportions was the highest in November 1999 and the lowest in December 2000. The specific activity of${eta}$-glucosidase divided by total bacteria was$1.6{ imes}10^5;amol{cdot}cell^{-1}{cdot}hr^{-1}$in August and$1.4{ imes}10^5;amol{ imes}cell^{-1}{ imes}hr^{-1}$in September while the specific activity divided by CTC active bacteria was about$3.6{ imes}10^5;amol{cdot}cell^{-1}{cdot}hr^{-1},;24.0{ imes}10^5;amol{cdot}cell^{-1}{cdot}hr^{-1}$. The specific activity of active bacteria in September was 6.7 times higher than that of August. By these data of active bacteria, the new information of aquatic ecosystem was unveiled.