Ethylenethiourea (ETU) is the common metabolite of the widely used ethylenebisdithiocarbamate fungicides. It is identified as Endocrine Disruptor given its ability to interfere with thyroid hormones biosynthesis by inhibiting thyroid peroxidase activity. As far as we know, no studies have been performed to assess potential effects of ETU exposure at low dose levels, i.e. below the established LOAEL and NOAEL, during critical phases of development. Therefore, the aim of the present study was to verify the short- and long-term effects on thyroid function, reproduction and development of oral exposure to ETU levels comparable to and lower than LOAEL/NOAEL in rats. Sixty dams were treated daily by gavage during pregnancy and lactation with 0, 0.1, 0.3, 1.0 mg/kg bw per day of ETU. F1 generation was similarly treated from weaning to sexual maturity. Thyroid biomarkers were analyzed in dams and in offspring. Reproductive biomarkers were analyzed in F1 rats. For the first time this study has demonstrated reproductive toxicity and hypothyroidism at a lower than LOAEL dose exposure in pregnant dams and F1 generation. Our data suggest that even low doses of ETU can interfere with thyroid homeostasis and reproductive hormone profile if exposure starts in critical stages of development.