Objective: To investigate the chemical constituents of the sponge Plakortis simplex from the south China sea. Method: Column chromatography on silica gel

reversed-phase silica gel (ODS)

Sephadex LH-20 and high performance liquid chromatography (HPLC) was used to study the chemical constituents of the sponge P. simplex collected from the south China sea. The structures of these compounds were elucidated on the basis of physicochemical and spectral analysis. Result: Seven compounds were isolated from the methanol extract of P. simplex

and their structures were identified as (22E)-5α

8α-epidioxyergosta-6

22-dien-3β-ol (1)

indole-3-carboxylic acid (2)

indole-3-carboxaldehyde (3)

monotriaj-aponide A (4)

methyl(2Z

6R

8R

9E)-3

6-epoxy-4

6

8-triethyl-2

4

9-dodec-atrienoate (5)

methyl(2Z

6R

8S)-3

6-epoxy-4

6

8-triethyldodeca-2

4-dienoate (6)

methyl (2Z

6R

8S)-4

6-diethyl-3

6-epoxy-8-methye(7). Conclusion: 7 compounds were isolated from P. simplex for the first time.