This paper reports on the cost-effectiveness of pedometer-based versus time-based Green Prescriptions in improving physical activity and health-related quality of life (EQ-5D) in a randomised controlled trial of 330 low-active, community-based adults aged 65 years and over. Costs, measured in $NZ (NZ$1=A$0.83, December 2008), comprised public and private health care costs plus exercise-related personal expenditure. Based on intention-to-treat data at 12-month follow up, the pedometer group showed a greater increase in weekly leisure walking (50.6 versus 28.1min for the time-based group, adjusted means, P=0.03). There were no significant between-group differences in costs. The incremental cost-effectiveness ratios, for the pedometer-based versus time-based Green Prescription, per 30min of weekly leisure walking and per quality-adjusted life year were, (i) when including only community care costs, $115 and $3105, (ii) when including only exercise and community care costs, $130 and $3500, and (iii) for all costs, -$185 and -$4999, respectively. The cost-effectiveness acceptability curves showed that the pedometer-based compared with the time-based Green Prescription was statistically cost-effective, for the above cost categories, at the following quality-adjusted life year thresholds: (i) $30000; (ii) $30500; and (iii) $16500. The additional program cost of converting one sedentary adult to an active state over a 12-month period was $667. The outcomes suggest the pedometer-based Green Prescription may be cost-effective in increasing physical activity and health-related quality of life over 12 months in previously low-active older adults.