Leveraging multiple interfaces (e.g., WiFi and cellular) on mobile devices is known to provide performance gains for applications such as bulk data transfer. In this paper, we complement prior studies by conducting, to the best of our knowledge, the first measurement study of mobile web performance over multipath TCP (MPTCP). Based on experiments using real web pages under diverse settings, we found the upper-layer web protocols can incur complex and sometimes unexpected interactions with the multipathenabled transport layer. MPTCP always boosts SPDY while may hurt HTTP. MPTCP also helps mitigate SPDY's key limitations of being vulnerable to losses and inefficient bandwidth utilization. We provide in-depth explanations of the root causes, as well as recommendations for improving mobile web performance over MPTCP.