Beta-1,3-glucanosyltransferase (Gas1p) plays important roles in cell wall biosynthesis and morphogenesis and has been implicated in DNA damage responses and cell cycle regulation in fungi. Yeast Gas1p has also been reported to participate in endoplasmic reticulum (ER) stress responses. However, the precise roles and molecular mechanisms through which Gas1p affects these responses have yet to be elucidated. In this study, we constructed deficient () and -overexpressing () yeast strains and observed that the strain exhibited a decreased proliferation ability and a shorter replicative lifespan (RLS), as well as enhanced activity of the unfolded protein response (UPR) in the absence of stress. However, under the high-tunicamycin-concentration (an ER stress-inducing agent; 1.0 g/mL) stress, the yeast cells exhibited an increased proliferation ability compared with the wild-type yeast strain. In addition, our findings demonstrated that and (two upstream modulators of the UPR) are required for the survival of yeast cells under the tunicamycin stress. On the other hand, we provided evidence that the overexpression caused an obvious sensitivity to the low-tunicamycin-concentration (0.25 g/mL). Collectively, our results indicate that Gas1p plays an important role in the ageing and ER stress responses in yeast.