The high incidence of oral cancer in Asian countries and South Pacific islands seems to be closely related to the widespread habit of betel quid chewing. Therefore the cytotoxity of betel quid ingredi-ents has become the focus of study. The purpose of our study was to reveal the mutagenicity and carcinogenicity of betel quid ingredi-ents with SOS thromotest 80S chromotes is the chromotest for the bacteria of genotoxins, the mechanism is that we detect the in-duction by the sifA gene which was controlled by Lex A (SOS sys-tem Repressor over the E. coli PQ37DNA). The samples were classified in three groups as follows, the first group was synthetic arecoline, arecaindine and tannin. The sec-ond group was arecoline extracted by the Scutt method. The third group was crude extract of betel quid and its ingredients. Quantita-tively we studied the amounts of r3 -Galactosidase and the SOS jn-duction factor to rE1veal the mutagenic potency. The results of the experiments showed that both arecolin and arecaindine are of mutagenic potency. Tannin possesses the least mutagenicity. Arecolin extracted by the Scutt method also has mu-tagenicity which is higher than that of both tannin and arecaindine. Among the various crude extracts of betel quid ingredients, betel quid had the highest SOS induction factor (mutagenic potency) with out“S-9 Mix” activation, unripped pipper line was second to the be-tel quid, otherwise betel leaves showed no mutageni potency. The mutagenicity potency of betel nut increase under the activation of“S-9 Mix” the mutagenicity of slaked lime and calcium hydroxide was not clear, but after activation of“S-9 Mix” the SOS inducting factor of calcium hydrate was stronger than slaked lime. In conclusion, we have demonstrated the mutagenic potency in the extracts of betel quid ingredients.