PURPOSE: This study investigates the effect of changes in moderate or vigorous physical activity (MVPA) on trajectories in health-related quality of life (HR-QoL) over 7 years in British elderly women. METHODS: A total of 1,926 women from the British Women's Heart and Health Study with information on MVPA and HR-QoL [measured using Euro quality of life 5 dimension (EQ-5D)] at baseline and at 7 years of follow-up were included in the analysis. Baseline and 7-year follow-up MVPA values were categorised into 3 groups, generating 9 categories of change in MVPA. Logistic regression was used to obtain odds ratios (ORs) of maintaining or improving HR-QoL according to different patterns of change in MVPA level. RESULTS: Women who remained inactive over the 7 years of follow-up had the largest reduction in their EQ-5D scores. Compared to these women, women that increased their MPVA level from "inactive" to "low" or to "moderate-high" were more likely to maintain or improve their HR-QoL over 7 years (ORs 1.65 or 2.70, respectively, p value for trend <0.001). After adjustment for baseline EQ-5D score and a wide range of potential confounders, results remained largely unchanged, though precision of the estimates generally decreased. CONCLUSIONS: Our findings suggest that relatively regular MVPA, even taken up later in life, can help older women prevent a decline in HR-QoL and even improve their enjoyment of life.