Background: Weight gain modifies body geometry by adding mass to different areas of the body. Objectives: The aim of this study was to determine the effect of body mass index (BMI) groups on postural stability of elderly females in a quiet stance by measuring the center of pressure (CoP) velocity. Methods: This quasi-experimental study consisted of 77 inactive females over 65 years old (67.7 ± 3.5) who had come to the Sports Medicine Center (Kiev, Ukraine) in the summer of 2017. All participants were classified into normal, overweight, and obese groups based on BMI. Postural stability was taken in a quiet stance (static situation) on a foam mat with open (OE) and closed (CE) eyes in anteroposterior (AP) and mediolateral (ML) directions by the force platform. Each test was performed two times for 30 seconds, and CoP was recorded at a sampling rate of 200 Hz. Results: In the AP direction, obese females swayed significantly faster than females with normal weight during OE (1.1 cm/s and 0.84 cm/s, respectively) and CE (1.2 cm/s and 0.88 cm/s, respectively) conditions. In the ML direction, higher CoP velocities in females with normal weight were observed than in obese females under OE conditions (0.55 cm/s and 0.43 cm/s, respectively) and CE (0.76 cm/s and 0.56 cm/s, respectively). Conclusions: Obesity had a negative influence on postural stability in the AP direction. However, given the expansion of the support base, obese females were more stable than normal-weight females along the ML direction. Study outcomes can be useful for obese people, medical staff, and healthcare decision-makers.