<p>Academic cheating among high school students remains a pressing concern, particularly in highly competitive academic settings. Teacher credibility, defined as students’ perceptions of a teacher’s competence, caring, and trustworthiness, has been proposed as a key deterrent to dishonest behavior; however, its role across different levels of academic competition remains insufficiently understood. The present research examined whether and how perceived teacher credibility influences students’ propensity to cheat in competitive academic contexts and whether these effects differ when credibility is based on real versus imagined teacher credibility. A 4 (academic competition: High competition, Medium competition, Low competition, Without competition) × 3 (teacher credibility: High credibility, Low credibility, Control) between-subjects design was implemented. Study 1 elicited teacher credibility through real experiences by prompting participants to recall actual teacher interactions. In Study 2, teacher credibility was manipulated using written materials that described imaginary teachers. Two independent samples of Chinese high school students (<i>N</i> = 244 for Study 1; <i>N</i> = 246 for Study 2) participated. In Study 1, a significant interaction between academic competition and teacher credibility was observed, such that competition showed an inverted U-shaped association with cheating under conditions of high teacher credibility. By contrast, Study 2 yielded a different pattern of results. Higher imagined teacher credibility was associated with higher test scores, although this effect was not consistently observed across all cheating indicators. These findings highlight the importance of developing authentic teacher credibility through genuine teacher–student relationships. Merely presenting credible authority figures in the absence of genuine rapport may have unintended adverse effects, particularly in increasingly competitive academic environments.</p>