Abstract: The transparent exopolymer particles(TEP), a kind of transparent colloidal particulate matter, consists of extracellular polysaccharides. TEP is of great significance to the carbon cycle of marine ecosystems. In this study, two marine diatoms, Ditylume brightwelii and Chaetoceros affinis, were studied. The TEP concentration, the relationship between TEP and Chlorophyll a (Chl a) and the C∶N ratio of TEP were studied at different growth phases. The results showed that TEP was produced by both species during the whole growth phases, and TEP concentration was different in different growth phase. The maximum TEP concentration of D. brightwelii and C. affinis was produced in the exponential phase and the decline phase, respectively. The maximum TEP concentration per cell volume and per Chl a of C. affinis was 184.91±14.03 fg Xeq/μm³ and 38.06±4.96 μg Xeq./μg Chl a, and were 16 and 5 times higher than the values obtained from the D. brightwelii. The analysis of the relationship between Chl a and TEP in two diatoms showed that the function relationship between TEP=α (Chl a) ^β was presented in the exponential phase (D. brightwelii: R²=0.98; C. affinis: R²=0.80). The TEP C∶N ratio of both diatoms was higher than the Redfield ratio (C∶N=106∶16). It indicates that the generation of TEP was difference between species, and the growth phase significantly affects the efficiency of TEP production. The high carbon concentration of TEP show that TEP production contributes significantly to the ocean carbon cycle.