Abstract: Solution culture experiment was adopted to investigate the influence of different nitrogen forms on lettuce growth and development and their nitrogenous nutritional characteristics. The results showed that the affinity of the roots of lettuce seedlings to ammonium nitrogen (NH₄⁺-N) was slightly higher than that to nitrate nitrogen (NO₃^--N). Among three treatments of NO₃^--N, NH₄⁺-N+NO₃^--N and NH₄⁺-N, the relative proportion of biological yields of lettuce was 100:56.9:12.4, and that of nitrogen uptake amount was 100:48.9:8.6, respectively. Nitrate nitrogen was the most suitable Nsource to lettuce growth. When the respective proportion of NH₄⁺-N and NO₃^--N was 50%, the growth of lettuce was inhibited to some extent. When the nitrogen source supplied as solely NH₄⁺-N, lettuce was hard to grow normally. When supplying the same amount of NH₄⁺-N and NO₃^--N, lettuce showed a tendency to absorb more NH₄⁺-N than NO₃^--N. At different culture stages, the ratio of NH₄⁺-N to NO₃^--N absorbtion was less than1. It seemed that lettuce did prefer NH₄⁺-N to NO₃^--N in absorbtion. However, ammonium nitrogen as nitrogen source was not suitable to lettuce for its metabolism. When nitrate nitrogen was not sufficient, it mainly affected the growth of lettuce shoot; when the ammonium nitrogen in nutrient solution was 50%, the root growth of lettuce seedlings was greatly inhibited, and some pathological symptoms appeared. Taking running water as water source (in which, NO₃^--N concentration was about 0.5 mol稬^-1) and lettuce was cultured by supplying sole NO₃^--N for two weeks and then supplying NH₄⁺-N, the growth of lettuce was greatly stimulated, in the meantime, the NO₃^--N contents and total accumulation amount greatly decreased. Supplying urea as Nsource, the growth rate of lettuce was apparently inferior to other nitrogen forms, but no pathological symptoms appeared.