Obestatin has been proposed to have anorexigenic and anti-ghrelin actions. The objective was to study obestatin concentrations in relation to handgrip strength, functional capacity and cognitive state in old women. The prospective study included 110 women (age, 76.93 ± 6.32) from the Mataró Ageing Study. Individuals were characterized by anthropometric variables, grip strength, Barthel and assessment of cognitive impairment [Mini Cognoscitive Examination (MCE) Spanish version], depressive status by the Geriatric Depression Scale (GDS) and frailty by the Fried criteria. Obestatin was measured by IRMA. Obestatin showed negative correlation to handgrip at basal time point (r = -0.220, p = 0.023) and at 2-year follow-up (r = -0.344, p = 0.002). Obestatin, divided into quartiles, showed a negative lineal association with handgrip: 11.03 ± 4.88 kg in first, 8.75 ± 4.08 kg in second, 8.11 ± 3.66 kg in third and 7.61 ± 4.08 kg in fourth quartile (p = 0.018). Higher obestatin levels were associated to increased weakness (categorized by handgrip of frailty criteria): 2.24 ± 0.42 ng/ml in weak vs. 1.87 ± 0.57 ng/ml in non-weak (p = 0.01). The decrease of either MCE or Barthel scores at 2-year follow-up was significantly higher in individuals in the fourth quartile of obestatin in comparison with individuals in the first quartile (p = 0.046 and p = 0.019, respectively). No association was found between obestatin and GDS score and neither with frailty as a condition. Obestatin is associated to low muscle strength, and impaired functional and cognitive capacity in old women participating in the Mataró Ageing Study.