Purpose: Instant messaging (IM) is one kind of online chat that provides real-time text transmission over the Internet. It becomes one of the popular communication tools. Even it is currnetly an era of smartphones, it still a great challenge to teach and promote the elderly to use smart phone. Besides, the acceptance of the elderly to use IM remains unknown. This study describes the usability and evaluates the acceptance of the IM in the elderly, who use the smartphone for the first time. This study is a quasi-experimental design study. The study period started from October, 2012 to December, 2013. There were totally 41 elderly recruited in the study. All of them were the first time to use LINE app on the smartphones. The usability was evaluated by using the Technology Acceptance Model which consisted of four constructs: cognitive usability, cognitive ease of use, attitude and willingness to use. Overall, the elderly had the best “attitude” for LINE APP communication software, with the highest rating averaging 4.07 points on four constructs, followed by an average of 4 points on “cognitive usefulness”. The socres of “cognitive ease of use” and “willingness to use” scores were equal which are an average score of 3.86. It can be interpreted that (1) the elders thought that the LINE APP as an excellent communication tool for them; (2) they found the software is useful (3) it was convenient for them to communicate. However, it was necessary to additionally assist and explain the certain functions such as the options. It would play a great role in the “willingness to use”. The positive acceptance of LINE APP in elderly refer to the probable similar acceptance for them to use other communication software. Encouraging the willingness the elderly to explore more technology products and understanding their behavior will be the basic knowledge to develop further software.