rtemisinin, a well-known antimalarial sesquiterpene lactone present in the plant Artemisia annua L. (Qinghao), was investigated for its yield improvement in the plant. Various mutants of A. annua were generated by gamma ray irradiation and propagated by using plant tissue culture techniques. A simple TLC-densitometric technique was developed for rapid analysis of artemisinin content in more than 200 samples of the obtained mutants. This new analytical method is based on the structural conversion of artemisinin on a silica gel plate by a NH3 to form a chromophore-containing compound that can be detected by UV-based TLC-densitometric analysis. Structure elucidation of the NH3-treated artemisinin product indicated that compound was 10-azadesoxyartemisinin which has its lambda max at 320 nm. Various crude extract samples of A. annua mutants were subjected to artemisinin separation on a silica gel plate using the solvent system of hexane: ethylacetate:acetone, 80:5:5. The TLC plate was then exposed with ammonia vapor at 100ํC for 2 hours before being scanned by TLC-densitometer using the wavelength of 320 nm. The technique appeared to be accurate and sensitive as compared with a complicated HPLC-UV technique. Among 205 mutant samples tested, the artemisinin content appeared to be highly variable, ranging from 0.02 to 3.46 % w/w of their dry weight of the crude extracts. Study on the enzyme activity of amorpha-4,11-diene synthase (ADS) showed a correlation between this enzyme activity and the artemisinin content for a number of mutants. This confirms that amorpha-4,11-diene synthase is important in the production of artemisinin in A. annua. The selected mutants with varied artemisinin content also showed essentially a correlation with their antimalarial activity. However, a few mutants with high antimalarial activity but low artemisinin content were also observed. An extra spot of compound was detected in these mutants and it might be another compound responsible for the antimalarial activity.