SOM encodes a nucleus-localized CCCH-type zinc finger protein and negatively regulates seed germination in Arabidopsis thaliana. We have previously demonstrated that ectopic expression of Sl ABI3, an important transcription factor in abscisic acid(ABA) signaling pathway, resulted in alteration of Sl SOM expression patterns in both leaf and seed of tomato. In this study, we aimed to elucidate the function of tomato Sl SOM in regarding to seed germination and seedling development. Here, we constructed Sl SOM over-expression vector p BI121-SOM driven by Ca MV 35 S promoter, and the recombinant plasmid was incorporated into wild-type tomato by the method of Agrobacterium tumefaciens-mediated transformation. The result showed that over-expression of Sl SOM conferred enhanced responses to exogenous ABA application during seed germination and seedling development. In addition, ectopic expression of Sl SOM resulted in the alteration of expression level of ABA/GA(gibberellins) metabolic genes, such as Sl ABA1, Sl CYP707A1, Sl GA3ox2, and Sl GA2ox4, in both leaf and seed. The ABA anabolic gene Sl ABA1 and the GA catabolic gene Sl GA2ox4 were up-regulated while the ABA catabolic gene Sl CYP707A1 and the GA anabolic gene Sl GA3ox2 were down-regulated. Compared to wild type, the expression level of Sl ABI5 was increased by about 40–50% in transgenic seeds while adding exogenous ABA treatment. These results support the notion that Sl SOM inhibits seed germination by regulating ABA/GA metabolic genes and Sl ABI5 expression in Solanum lycopersicum. SOM encodes a nucleus-localized CCCH-type zinc finger protein and negatively regulates seed germination in Arabidopsis thaliana. We have previously demonstrated that ectopic expression of Sl ABI3, an important transcription factor in abscisic acid (ABA) signaling pathway, resulted in alteration of Sl SOM expression patterns in both leaf and seed of tomato. In this study, we aimed to elucidate the function of tomato Sl SOM in regarding to seed germination and seedling development. Here, we constructed S1 SOM over-expression vector p BI121-SOM driven by CaMV 35 S promoter, and the recombinant plasmid was incorporated into wild-type tomato by the method of Agrobacterium tumefaciens-mediated transformation. The result showed that over-expression of S1 SOM conferred enhanced responses to exogenous ABA application during seed germination and seedling development . In addition, ectopic expression of S1 SOM resulted in the alteration of expression level of ABA / GA (gibberellins) metabolic genes, such as Sl ABA1, Sl CYP707A1, Sl GA3ox2, and Sl GA2ox4, both in leaf and seed. The ABA anabolic gene S1 ABA1 and the GA catabolic gene S1 GA2ox4 were up-regulated while the ABA catabolic gene S1 CYP707A1 and the GA anabolic gene Compared to wild type, the expression level of S1 ABI5 was increased by about 40-50% in transgenic seeds while adding exogenous ABA treatment. These results support the not that that S1 SOM inhibits seed germination by regulating ABA / GA metabolic genes and Sl ABI5 expression in Solanum lycopersicum.