Although a substantial body of mentoring research has been conducted on students attending four-year colleges, the interplay of career-related mentoring, ambiguity tolerance, and job search effort and behavior has not been seriously investigated. Therefore, we examined the relationship between career-related mentoring and ambiguity tolerance, as well as job search effort and behavior, for the purpose of understanding how to better assist undergraduate college students achieve preliminary job search success. Data were collected via pencil surveys administered to 300 undergraduate students selected by purposive sampling from four colleges in Seoul, Korea. Correlation analysis and covariance structure analysis were conducted to examine the relationships between variables. A Sobel test was also conducted to check the mediation effect of the model. Results were consistent with our hypotheses and showed that there was a significant, indirect, positive effect of career-related mentoring on job search effort and behavior, mediated through ambiguity tolerance. Our study contributes to career-related mentoring and job search research by providing empirical evidence supporting the results. It has implications for universities, mentoring program design, and career guidance professionals.