Older adults have been recognized as the most sedentary age group globally and although a growing body of literature has emerged surrounding older adults' motives to limit sedentary behaviour, little has been done to develop practical tools to evaluate these motives. In response, a pool of 41 items was developed using information gathered during focus groups rooted in self-determination theory from older adults and a scoping literature search. The 41 items were then presented to 319 older adults (52.4% women, Mage = 71.92; SD = 5.71) in an online survey and the obtained responses were used to assess the factorial validity and internal consistency of the items. Data analysis was conducted using exploratory structural equation modelling. Following the removal of eight problematic items the following fit indices were identified: ?2(345) = 586.739, p < 0.001; CFI = 0.952; TLI = 0.926; SRMR = 0.026; and RMSEA = 0.047 (90% confidence interval = 0.040, 0.053) with most items loading ? 0.32 on the intended factor. Additionally, internal consistency (Cronbach's ?) for the six factors were as follows: intrinsic motivation = 0.90; integrated regulation = 0.91; identified regulation = 0.89; introjected regulation = 0.85; external regulation = 0.64, and; amotivation = 0.83. Though these results demonstrate promise for an instrument based on an established theoretical framework for evaluating older adults' motives to sit less; additional investigations are needed to improve item quality for the external regulation subscale and further determine the test-retest reliability and criterion validity of the items.