Due to the complex registration & downloading process of the native applications, and, software and their non-standardized APIs, mobile web application is now being an alternative software for smartphones. Hybrid web application, one of the types of mobile software, because develop and has reasonable performance by using the webkit engined in smartphones. It can be easily developed by using the exiting programming skill such as HTML, JavaScript and CSS. Additionally these programming techniques can be easily used in any smartphone regardless of its platforms. Most smartphones have a webkit engine or web rending engine for high performance and smooth display in web browser. Webkit is now equipped in iPhone and Android phone. In this paper, we try to find out by comparison that the various aspects of webkit APIs of iPhone & Android phone, such as screen font size, screen orientation, touch event, gesture event and their performance. We also evaluated which one is more convenient for developers when making web programs using webkit. As a result, we found out that webkit in iPhone has more excellent performance than Android.