This study is an extension of Nahatame's (2018) research that demonstrated the effects of causal and semantic relations between sentences on second language (L2) text processing. Employing eye tracking, this study aimed to examine whether these effects appear during more natural, uninterrupted reading processes and to identify the time course of the effects. In the experiment, Japanese learners of English read two-sentence texts that varied in their causal and semantic relatedness, as evaluated by crowdsourced human judgments and via a computational approach (latent semantic analysis), respectively. Two eye-movement measures were collected and analyzed: first-pass reading times for the second sentence and lookbacks from the second to the first sentence. The results indicated that causal relatedness had a robust impact on both reading times and lookbacks. However, semantic relatedness impacted only reading times, and its effects were modulated by causal relatedness. Theoretical, pedagogical, and methodological implications of this finding were discussed.