L2 syntactic processing researches have been conducted for the purpose of elucidating the cognitive mechanisms, processes and strategies used by L2 learners. However, there have been fewer ones regarding comparison of the Japanese senior high school students’data and University students’data with a special reference to the significant effects of the prior discourse contexts on ambiguity resolution of syntactic structures. The principal aim of the present research can be defined as an experimental attempt to investigate whether there are significant differences between the results in this study and those in series of our previous studies. The results of the present study are as follows: １） Regarding the effects of prior discourse context on syntactic ambiguity resolution, the difference of 9% between the percentage correct for stimulus sentences (27%) and the stimulus sentences with a prior discourse contexts (36%) was statistically significant (t=4.07, df=37, p<.01) in this study. This finding supports the results in series of our previous studies. ２） Regarding which information factor is the most significant one among syntactic, semantic, and discourse information for Japanese EFL learners’accurate processing, one-way ANOVA revealed a significant difference between average scores for the three factors (F(2,78)=6.791, p<.01). Tukey’paired comparison test showed that the difference between syntactic and semantic information was significant (p<.01). These findings display that the participants preferentially adopted prior discourse contexts. These results also support those of a series of our previous studies.