The nuclear factor of activated T cell cytoplasmic 1 (NFATc1) is a member of the NFAT family and is strictly implicated in the growth and development of bone. Most studies have focused on the effects of NFATc1 activation on osteoclastogenesis. On the contrary, the specific roles of NFAT in osteoblast differentiation are not well understood and, in some instances, reports of its role are contradictory. In the present study, we demonstrated that NFATc1 was involved in the transcriptional regulation of human estrogen receptor alpha (ERalpha) gene in SaOS-2 osteoblastic like cells. NFATc1 was specifically recruited "in vivo" at C and F distal promoters of ERalpha gene. In addition, it is here identified as the negative transcription factor removed by the RA4-3'decoy oligonucleotide able to induce ERalpha expression in osteoblasts. Ca(2+)/calcineurin-NFAT-mediated signaling pathways and ERalpha-dependent signals are involved in diverse cellular reactions by regulating gene expression under both physiological and pathological conditions. Therefore, our data might be useful for proper manipulation of NFATc1- and ERalpha-mediated cellular reactions in different bone disorders, such as osteoporosis.