Telomerase is a ribonucleoprotein complex that elongates telomeres, allowing to stabilize the ends of chromosomes during cell proliferation. Here nested PCR method was used to describe the transcriptional patterns of mTERT (mouse telomerase reverse transcriptase) gene, encoding the catalytic subunit of mouse telomerase expressed both in murine adult tissues and preimplantation embryos cultured in CZB medium from zygote to blastocyst. The analysis revealed that the mTERT mRNA expression in adult tissues, such as testis, spleen, kidney, liver, and thymus. For single-copy zona-free oocyte or embryo samples, the tert transcript in 60% (6/10) of matured oocytes (15 h-post hCG) had been not found, while the transcripts of housekeeping gene hprt located in all matured oocytes (10/10). No tert mRNA was present in single-copy embryo samples at early (20 h-post hCG, 6/6), late (30 h post-hCG, 8/8) pronuclear stage, or early 2-C stages (35 h-post hCG, 7/7), although the hprt mRNA transcriptions were found during this period. Interestingly, the embryos at early 2-C stage expressed of tert and hprt gene together in multi-copy (20 embryos/sample) embryo samples. Half of single-copy embryos (4/8) shown expression of two genes simultaneous at late 2-C stage (50 h-post hCG), while the other half of them (4/8) only transcript either tert (2/4) or hprt gene (2/4). Expression of tert and hprt genes were detected simultaneous in all single-copy embryos developed at 4-C (65 h-post hCG, 4/4), 8-C (75 h-post hCG, 4/4), morulae (93 h-post hCG, 4/4) and blastocyst (118 h-post hCG, 4/4) stages and the level of transcription increased. These results suggested that tert gene was began to express in embryos at early 2-C stage during the process of embryonic genome activation and the level of transcription was increased during embryogenesis.