Triggering receptor expressed on myeloid cells (TREM) like transcript-1 (TLT-1) is an immunoreceptor tyrosine-based inhibitory motif (ITIM)-baring TREM family protein. In this study, we identified an alternative transcript of TLT-1, namely TLT-1s, which has very short extracellular immunoglobulin (Ig) domain (202 amino acids). TLT-1s was mainly expressed in macrophages and osteoclast precursor cells. Upon RANKL stimulation, TLT-1s mRNA and protein levels were gradually decreased in BMMs. Significantly, silencing of TLT-1s strongly enhanced the formation and resorption activity of osteoclast, while forced expression of TLT-1s reduced osteoclast formation.