To investigate the cellular growth traits of a photosynthetic green algae, Chlorella pyrenoidosa, several tests upon a culture temperature, a culture time, the influence of nutrient and the intensity of illumination were executed. Using growth chamber, some optimal conditions for the culture of algae were as follows: The culture temperature was about $28^{circ}C$, the culture time about 4 days, and the cellular growth of algae was in proportioned to the concentration of nutrient such as nutrient broth. And the more the intensity of illumination was increased, the more the algal cell showed good growth. And then, the activity of enzyme degrading acetaldehyde was also studied using HPLC from the same strain. This enzyme was dependent on $eta$-$NAD^+$. And showed its optimal pH around on 9.0, and also its optimal temperature around at $40^{circ}C$. The operational conditions of HPLC were as follows: Column, ODS-Hypersil ; mobile phase, 50% (v/v) acetonitrile.