BACKGROUND: Older workers are less physically active and have a higher rate and cost of injury than younger workers and so have reduced work-ability. Concurrently, sedentary behaviour in the workplace, in transport and in the home is increasing and has harmful health effects. Walking is a familiar, convenient, and free form of health-enhancing physical activity that can be integrated into working life and sustained into older age however workplace walking programs targeted at older workers have not been evaluated. PURPOSE: We designed a randomised-controlled trial to evaluate the impact of a phased individually-tailored 10-week walking program on work-day steps, health status and work-ability of employees at an Australian university with an ageing sedentary workforce. METHODS: A convenience sample of 154 academic and administrative employees aged 45-70 years will be recruited and randomly allocated to either an experimental (walking) group or control (maintain usual activity) group. Participants will be provided with a pedometer and complete measures for step count, % body fat, waist circumference, blood pressure, self-reported physical activity, psychological wellbeing and work-ability, at baseline and end-intervention. 'Walkers' will select approaches tailored to their individual preference, psychological characteristics or life circumstances. Two distinct intervention phases will target adoption (weeks 2-5) and adherence (weeks 7-12) using 'Stages of Behaviour Change' principles. An ANOVA will test for effect of treatment on outcome with the baseline value entered as a covariate. DISCUSSION: This study will test whether tailoring worksite walking is an effective means of promoting health-enhancing physical activity in ageing sedentary workers.