Along with the development of technology at this time some programmers have found a solution to overcome the problem of storing important files that we worried about before the file security by making several applications that we often refer to as online file storage. Files saved to online file storage are usually document files and image files. However, the problem that arises is the image file has a large size and takes up large storage space and requires a long time in the process of exchanging data. To reduce the size of an image file compression techniques can be used. Compression is a way to compress data so that it only requires a smaller storage space so that it is efficient in storing or shortening time in exchanging information. Compression technique has several algorithms, in this study the authors used the Adaptive Arithmetic Coding algorithm. From the results of the study the authors managed to compress a color image file with jpg extension using the Adaptive Arithmetic Coding algorithm. The application produced in this research is a web designed using Dreamweaver CS5 and php programming language.Keywords: Compression, Adaptive Arithmetic Coding, DreamweaverCS5, PHP.