From September 1992 to August 1993, nitrogen assimilation and mineralization along with selected biological and physico-chemical environmental factors were investigated 9 times at two different stations in Lake Soyang. For the analysis of assimilation and mineralization, ion concentration analysis method was used. The range of nitrogen assimilation and mineralization rates were 0-100.6㎍-N L^-1 day^-1 and 0∼130.3㎍.-N L^-1 day^-1·respectively. At station 1. where was influent area, assimilation rate which was measured in the surface was correlated positively with temperature (r=0.82. p<0.01) and variation of ammonia (r=0.70, p<0.05) and it was correlated with chlorophyll-a (r=0.87, p<0.01) and nitrate (r= -0.75, p<0.05) in bottom against surface. At station 2, where was Joined with main and influent stream, assimilation rate in surface was correlated with temperature(r=0.77, p<0.05), pH (r=0.70,p<0.05) and ammonia (r=0.69, P<0.05) and mineralization rate in surface was positively correlated with temperature(r=0.86, p<0.01)and pH (r=0.84, p<0.01). Mineralization rate in bottom was correlated with N/P ratio (r=-0.67, p<0.05).