Purpose of the study: Previous research found that "fun on line" is the most dominant content in seniors' online communities. The present study aimed to further explore the "fun culture" in these communities and to discover its unique qualities. Design and Methods: The study applied an online ethnography (netnography) approach, utilizing a full year's data from 6 leading seniors' online communities. The final database included about 50,000 posts. Results: The majority of posts were part of online social games, including cognitive, associative, and creative games. The main subjects in all contents were sex, gender differences, aging, grandparenting, politics, faith, and alcohol. Main participatory behaviors were selective timing, using expressive style, and personalization of the online character. Although most participants were "lurkers," the active participants nurtured community norms and relationships, as reflected in the written dialogues. Implications: In a reality of limited alternatives for digital games that meet older adults' needs and interests, seniors found an independent system to satisfy their need for play. Seniors' online communities provided a unique form of casual leisure, whose nature varied among different groups of participants. The fun culture seemed to offer participants many desired benefits, including meaningful play, liminality and communitas, opportunity to practice and demonstrate their abilities, and means for coping with aging. Therefore, it may have positive impact on seniors' well-being and successful aging.