Purpose: The purpose of this study was to investigate the influences of job insecurity on job related depression and anxiety in large- and small-sized company employees. Methods: Data of the third Korean Working Condition Survey in 2011 were used. Subjects were 2,050 large-sized company employees and 18,924 small-sized company workers. $x^2$ test and multiple logistic regression using SAS 9.2 were conducted. Results: Large- and small-sized company employees showed significant differences in terms of demographic, health-related, and job-related characteristics. From the bivariate analysis, gender, income, self-rated health, occupation, working hours per week, job-related stress, workplace violence, and job insecurity were significantly related to job-related depression/anxiety in large-sized company employees. From the multivariate analysis, higher income (AOR: 0.22, 95%CI: 0.07~0.71), better health perception (AOR: 0.05, 95%CL: 0.01~0.18), 40 or more working hours per week (AOR: 0.20, 95%CI: 0.05~0.79) showed lower risk for job-related depression/anxiety. From the bivariate and multivariate analysis, better health perception (AOR: 0.32, 95%CI: 0.20~0.53), higher job-related stress (AOR: 2.57, 95%CI: 1.68~3.93, workplace violence experience (AOR: 4.26; 95%CI: 2.88~6.30), and job insecurity experience (AOR: 1.90, 95%CI: 1.18~3.05) were significantly related to job-related depression/anxiety in small-sized company employees. Conclusion: Results of this study suggest that job insecurity experience was significantly related to job-related depression/anxiety in small-sized company employees but not in large-sized company employees. Therefore, small-sized company workers who have experienced feeling of job insecurity are vulnerable population in terms of job-related depression/anxiety.