Physical activity has many physical and mental health benefits and can delay the development of disability in older age. However, uptake of this health behaviour is sub-optimal in women in their middle and older age. This trial aims to establish the acceptability and feasibility of the Active Women over 50 programme involving online information, telephone health coaching and email or SMS support to promote physical activity behaviour change among women aged 50 years and over. Sixty community-dwelling women who are insufficiently active according to national guidelines, will be recruited and randomised to 1) receive the Active Women over 50 programme or 2) a wait-list control. Active Women over 50 is a 3-month physical activity programme guided by behaviour change science, providing access to a website, one telephone-delivered health coaching session from a physiotherapist and 8 email or 24 SMS messages. The primary outcome is the proportion of participants at 3 months post-randomisation who would recommend participation in the programme to another person like themselves. Secondary outcomes are feasibility measures: rates of recruitment, retention, completeness of outcome data and uptake of telephone support; and intervention impact measures: accelerometer-assessed average steps/day, proportion of participants meeting national guidelines on moderate to vigorous physical activity; and questionnaire-assessed quality of life, exercise perceptions, mood, physical functioning and self-reported physical activity. Intervention participants will also complete a follow-up survey to assess impressions of the intervention and adoption of strategies for physical activity participation. Data will be analysed descriptively to guide the design of a larger trial. Between-group differences in secondary outcomes will be used to estimate effect sizes for sample size calculations for a fully powered randomised controlled trial. This feasibility pilot trial of an efficient eHealth and health coaching intervention guided by user input and behaviour change theory, will inform future interventions to address low physical activity participation among an under-active group at risk of future disability. ANZCTR, ACTRN12619000490178, registered 26 March 2019