Android application is an important class on today’s Internet. While understanding app-specific behavior is important for network operation and management, it is often difficult because it requires an in-depth application-layer protocol analysis due to the common use of HTTP(S) and standard data representations (e.g., JSON). this paper presents Extractocol the first system to offer an automatic and comprehensive analysis of application protocol behaviors. Extractocol only uses Android application binary as input and accurately reconstructs HTTP transactions (request-response pairs) and identifies their message format and relationships using binary analysis. Our evaluation and in-depth case studies on commercial and open-source apps demonstrate that Extractocol provides high coverage and accurately characterizes network-related application behaviors.