Malnutrition is common among older adults in health-care settings and is associated with decreased quality of life (QoL). The present study aimed to investigate the effect on health-related QoL (HRQoL) among older adults after 6 months of treatment with individual dietary advice (DA) and/or oral nutritional supplements (ONS), utilising 409 patients included in a multicentre randomised controlled trial of patients ≥ 65 years old, stratified according to nutrition status (malnourished/at risk of malnutrition), admitted to hospital in Sweden 2010–2014. Patients were randomised into four arms: DA, ONS, DA + ONS or routine care (control). The intervention started at discharge from hospital, with HRQoL measured using European QoL five-dimension, three-level (EQ-5D-3L) and European QoL-visual analogue scale (EQ-VAS) at baseline and at 6-month, 1-year and 3-year follow-ups. Data were analysed using the Kruskal–Wallis test and multiple linear regression. Overall, HRQoL increased from baseline to follow-ups, although the magnitude of change in EQ-5D-3L did not differ significantly between the four arms in any of the nutrition groups. However, a significant difference was observed for change in EQ-VAS from baseline to 6-month follow-up in the malnourished group, with mean changes of 22·4 and –3·4 points for the ONS and control groups, respectively (P = 0·009). In the multiple linear regression analyses, participants in the ONS arm had 27·5, 34·4 and 38·8 points larger increases in EQ-VAS from baseline to the 6-month (P = 0·011), 1-year (P = 0·007) and 3-year (P = 0·032), respectively, follow-ups than the control group. The use of ONS improved subjectively assessed HRQoL in these malnourished older adults.