Objectives: To provide experimental evidence by study on microleakage and compressive strength of four different fissure sealants.Methods:28 caries-free premolars extracted for orthodontic reasons from 12-16 years old volunteers were collected and randomly divided into 4 groups.Fissures were respectively sealed with Helioseal F、VOCO Fissurit F、AscentTM、ClinproTM pit and fissure sealant.Then the teeth were thermocycling for 100 times.5 teeth in each group were stained with 20mg/L methylene blue for 24 hours,and then were sectioned for evaluation of microleakage.2 teeth in each group were used for the observation of marginal adaptability of fissure sealants with tooth interface by SEM.9 disc-like specimens(with the thickness on 4mm diameter on 4mm)were prepared for each material and kept in normal saline at 37℃.The compressive strength,was examined 1 d,28 d and 63 d after saline treatment(N= 3).