LAG1 was identified as a gene that is differentially expressed during the yeast replicative life span and was shown to play a role in determining yeast longevity. The cDNA of rat LASS1, the mammalian homolog of yeast LAG1, was cloned from rat cerebral cortex and sequenced, which is different to the predicted sequence in the GenBank. Sequence analysis revealed that this cDNA clone contains an open reading frame of 1 053 bp. The deduced amino acid sequence has 350 residues and shares a predicted Lag1p motif and a TLC domain conserved in Lag1 proteins. Total RNAs were isolated from rat cerebral cortices at varying ages: newborn, one month, six months, twelve months, and twenty-four months. Semi-quantitative RT-PCR and Northern blot analysis were performed to analyze the LASS1 expression level in rat cerebral cortex tissues at varying ages. Senescence-associated β-galactosidase (SA-β-gal) activity was firstly used as a biomarker for assessing senescence in rat neurons. The results showed that LASS1 expression was upregulated from newborn to adult rats (1～6 month) and declined in aged cortex. SA-β-gal staining positive neurons significantly increased in the aged cerebral cortex. The age-related expression alternation of LASS1 in rat cerebral cortex provides an important clue in exploring the role of LASS1 in mammalian neuron aging.