Cognitive assessment with virtual reality (VR) may have superior ecological validity for older adults compared to traditional pencil-and-paper cognitive assessment. However, few studies have reported the development of VR tasks. The aim of this study was to present the development, feasibility, content validity, and preliminary evidence of construct validity of an ecological task of cognitive assessment for older adults in VR (ECO-VR). The tasks were prepared based on theoretical and clinical backgrounds. We had 29 non-expert judges identify virtual visual stimuli and three-dimensional scenarios, and five expert judges assisted with content analysis and developing instructions. Finally, six older persons participated in three pilot studies and thirty older persons participated in the preliminary study to identify construct validity evidence. Data were analyzed by descriptive statistics and partial correlation. Target stimuli and three-dimensional scenarios were judged adequate and the content analysis demonstrated that ECO-VR evaluates temporo-spatial orientation, memory, language and executive functioning. We made significant changes to the instructions after the pilot studies to increase comprehensibility and reduce the completion time. The total score of ECO-VR was positively correlated mainly with performance in executive function (r = .172, p < .05) and memory tests (r = .488, p ≤ .01). The ECO-VR demonstrated feasibility for cognitive assessment in older adults, as well as content and construct validity evidences.