Abstract: In this work, an electronic nose was used to evaluate the different mature stages of tomatoes and the ripening stages of mature, overmature tomatoes through their shelf lives. When the maturity was distinguished according to color, the score plot of the principal component analysis(PCA) and linear discriminant analysis (LDA) for the electronic nose measurement show that immature tomatoes can be distinguished from mature and overmature tomatoes. But the result is not good for mature and overmature tomatoes. Firmness was also applied to determine the maturity of tomatoes. When firmness was considered, the PCA can be used to classify 100% of the total samples at different mature stages. The result shows that the difference of firmness can be distinguished by electronic nose. The changes of two different mature state tomatoes were monitored during shelf life (1～11 d, 14 d, 17 d). Based on electronic nose, a clear distinction among mature tomatoes on 1～6 d, 7～11 d and 14～17 d is available. And it is also possible to distinguish overmature tomatoes on 1～5 d, 6～11 d and 14～17 d by using LDA.