Abstract: In the current study, to establish the standard system for assessing the activity and quality of larval Penaeus monodon, whose tolerance to drying, starving, sharply-decreased salinity and formalin were investigated by methodologies of visualizing, microscopy and virus detection. The results showed that healthy postlarvae were featured with phototaxis and gregariousness; their body-surface was clean and the tissue was transparent; the stomach and intestine were full. The appropriate time for postlarvae to live without water was 15 minutes. After that, healthy postlarvae resumed vitality quickly while the sick ones were dead or narcose. The survival rate of postlarvae decreased with an extention of starvation time, with an increase of concentration of formalin and time, as well as with an abrupt drop of salinity. Healthy postlarvae could sustain about 30 minutes in 100~200 μL·L^-1 formalin and the survival rate almost reached 100%. The appropriate range of salinity for postlarvae was 20~30, but they only sustained 1 hour in fresh water. Virus detection could avoid the outbreak of disease that might result from the postlarvae carrying with virus.