Vocabulary is the cornerstone of listening, speaking, reading, writing, translation and other language skills. According to statistics available, children learn about 3000 vocabularies per year during the primary school period, and about 30% of the vocabularies are acquired from the natural reading. That is, with the increasing exposures of the novel words to different sentential contexts, readers have gradually formed the novel lexical representation in their mental lexicon. Previous study has shown that adults could form the more consolidated lexical representation than children during the initial four encounters with different contexts based on their eye movement behaviors. In the present study, we endeavor to explore how reader’s eye movement behavior change during the initial several encounters when learning the novel words in the natural reading. Specifically, we focus on the issue of whether the change of reader’s eye movements show the developmental trends with the increasing number of encounters with different contexts. We adopted a group of high-frequency characters to construct 30 two-character pseudowords as novel words. Every target word was embedded into five sentence frames, each of which provided a context describing a plausible meaning of the pseudoword it contained. Each pseudoword was assigned to one of ten real-world semantic categories. In order to test whether or not readers had learned the semantic category of each pseudoword after reading it within five sentential contexts, a multiple choice semantic category question (presenting ten categories, of which five were used in the experiment and five were distractors) was presented to the participants. The eye movements of two groups of participants (including adults and 9-year olds) were recorded when they read the sentences. The first aspect of results showed that, children and adults undergo the same pattern of change on first fixation duration with the increasing reading of novel words through sentential contexts. That was, the duration of the first fixation located on the novel words sharply decreased when they met it for the second time, and it retained the same level during the next three encounters. It suggests that there is no developmental trend between children and adults in the very early stage of lexical processing when learning the novel words through context. Another aspect of results showed that, adults and children undergo different patterns of changes with the increasing reading of novel words through sentential contexts. For adult, gaze duration, refixation probability, and total reading time on the novel words sharply decreased when they read it in the second time; by contrast, children saved some gaze duration and refixations probability on the novel words in the fourth time of reading novel words within contexts, but it did not occur during the first three times of reading. These results indicates that adults showed better performance than children on the relative later stage of lexical processing when learning novel words through contexts.