Abstract-This paper reports the first quantitative comparison study of elastic and viscoelastic properties of oocytes from young and aged mice. A force measurement technique, including a poly(dimethylsiloxane) (PDMS) cell holding device and a sub-pixel computer vision tracking algorithm, is utilized for measuring forces applied to an oocyte and resultant cell deformations in real time during oocyte manipulation. To characterize elastic and viscoelastic properties of the oocytes, a stress-relaxation indentation test is performed. A two-step, large-deformation mechanical model is developed to extract the mechanical properties of the oocytes from the measured force-deformation data. The experimental results demonstrate that the aged oocytes are significantly softer (instantaneous modulus: 2.2 vs. 5.2 kPa in young oocytes) but more viscous (relaxation time: 4.1 vs. 2.3 s in young oocytes) than the young oocytes.