We propose a chatbot to assist cancer patients and their families with clinical trials information online. Clinical trials are important tools to improve knowledge about effective treatments for all diseases, including cancers. However, studies show that fewer than 5% of cancer patients are enrolled in any type of research study or clinical trial. Although there are a wide variety of reasons for the low participation rate, we address this issue by focusing on the difficulty of information acquisition and comprehension of clinical trial documents due to medical jargon and technical details. To reduce such difficulty, a chatbot was developed to answer questions and provide proactive assistance in a conversational manner. The chatbot is designed to help users determine whether they are eligible for the clinical trial and to identify what additional information that they need to consult with their doctors about in order to determine their eligibility. An in-person experiment was conducted to evaluate the effectiveness of the chatbot. First, information about a specific clinical trial on melanoma cancer was obtained from the National Cancer Institute. Three interfaces were developed: a traditional website mimicking NCI’s search page, a website containing the clinical trial information with a chatbot assistant in the sidebar, and a chatbot-only interface with information delivered only through the chatbot. The preliminary results indicate that the participants who used chatbots achieved better understanding about eligibility than those who used only the website. Additionally, interfaces with chatbots were rated significantly better in terms of perceived usability, interactivity, and dialogue.