This study employed eye-tracking technology to examine how students with different levels of prior knowledge process text and data diagrams when reading a web-based scientific report. Students' visual behaviors were tracked and recorded when they read a report demonstrating the relationship between the greenhouse effect and global climate change in 2 diagrams and 4 textual sections. Based on the pretest scores, 13 participants were categorized into high and low prior knowledge (PK) groups. Eye-tracking measures including the total reading time, total fixation duration, and total regression number on each area of interest of the 2 groups were compared. A heat map was further used to show the overall visual distribution of each group. In addition, the inter-scanning transitions between the textual and graphical information of the 2 groups were compared and further confirmed by the patterns of the scan paths. The results revealed that overall students spent more time reading the textual than the graphical information. The high PK students showed longer fixation durations and more regressions on the graphics than the low PK students. Meanwhile, the high PK students showed more inter-scanning transitions than the low PK students not only between the text and graphics but also between the 2 data diagrams. This suggests that the high PK students were more able to integrate text and graphic information and inspect scientific data which is essential for online inquiry learning. This study provides eye-tracking evidence to show that low PK students have difficulties integrating scientific diagrams with expository texts and inspecting scientific data diagrams that are commonly shown in websites. Suggestions are made for future studies and instructional design for online inquiry-based science learning.