Objective We aimed to explore the reliability and validity of the two shortened versions of the Metacognition Questionnaire-Insomnia (Metacognition Questionnaire-Insomnia-6 items [MCQI-6], Metacognition Questionnaire-Insomnia-14 items [MCQI-14]) among patients with cancer and examine the feasibility of the Discrepancy-Cognitive Arousal (DCA) model of insomnia among the cancer patients. Methods A total of 154 patients with cancer were enrolled in this survey, which included rating scales such as the discrepancy between desired time in bed and desired total sleep time (DBST) index, Insomnia Severity Index (ISI), Cancer-related Dysfunctional Beliefs and Attitude about Sleep-14 items (C-DBAS-14), MCQI-6, and MCQI-14. Results Both the MCQI-6 and MCQI-14 showed a good reliability of internal consistency. Confirmatory factor analysis showed a good model fit for two single-factor shortened versions. The total score of the MCQI-6 was significantly correlated with the MCQI-14 (r=0.97, p<0.01), ISI (r=0.68, p<0.01), C-DBAS-14 (r=0.78, p<0.01), and DBST index (r=0.21, p<0.05). Mediation analysis showed that the DBST index did not directly influence insomnia severity; however, the relationship was mediated by cancer-related dysfunctional beliefs about sleep and sleep-related metacognitive process among patients with cancer. Conclusion The Korean versions of MCQI-6 and MCQI-14 are useful, reliable, and valid tools to evaluate sleep-related metacognitive processes among patients with cancer. The DCA model of insomnia was feasible even among cancer patients.