A process for preparing artemisinin, comprising the steps of: - preparing a mixture comprising (i) a dihydroartemisinic acid derivative of 5 formula wherein - X is O; - Y represents a group of formula where R 3 is OR 1 and R 1 is a C 1 -C 12 alkyl group which is linear or branched or 15 a C 3 -C 10 cycloalkyl group, said alkyl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen, or a C 6 -C 14 aryl or heteroaryl group, said aryl or heteroaryl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen; (ii) at least one organic solvent and (iii) a photosensitizer selected from Rose bengal, tetraphenylporphyrin and tetraphenylporphyrin derivatives (TPP derivatives); - subjecting said mixture to photooxidation by means of a light source, and - recovering the artemisinin thus obtained. - preparing a mixture comprising (i) a dihydroartemisinic acid derivative of 5 formula wherein - X is O; - Y represents a group of formula where R 3 is OR 1 and R 1 is a C 1 -C 12 alkyl group which is linear or branched or 15 a C 3 -C 10 cycloalkyl group, said alkyl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen, or a C 6 -C 14 aryl or heteroaryl group, said aryl or heteroaryl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen; (ii) at least one organic solvent and (iii) a photosensitizer selected from Rose bengal, tetraphenylporphyrin and tetraphenylporphyrin derivatives (TPP derivatives); - subjecting said mixture to photooxidation by means of a light source, and - recovering the artemisinin thus obtained. (i) a dihydroartemisinic acid derivative of 5 formula wherein - X is O; - Y represents a group of formula where R 3 is OR 1 and R 1 is a C 1 -C 12 alkyl group which is linear or branched or 15 a C 3 -C 10 cycloalkyl group, said alkyl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen, or a C 6 -C 14 aryl or heteroaryl group, said aryl or heteroaryl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen; - X is O; - Y represents a group of formula where R 3 is OR 1 and R 1 is a C 1 -C 12 alkyl group which is linear or branched or 15 a C 3 -C 10 cycloalkyl group, said alkyl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen, or a C 6 -C 14 aryl or heteroaryl group, said aryl or heteroaryl group being unsubstituted or substituted by one or more substituent(s) selected from a C 1 -C 6 alkyl group and a halogen; (ii) at least one organic solvent and (iii) a photosensitizer selected from Rose bengal, tetraphenylporphyrin and tetraphenylporphyrin derivatives (TPP derivatives); - subjecting said mixture to photooxidation by means of a light source, and - recovering the artemisinin thus obtained. - subjecting said mixture to photooxidation by means of a light source, and - recovering the artemisinin thus obtained.