Colorectal cancer is second leading cause of cancer death. There have been many approaches proposed, such as anti-cancer drugs, chemotherapy and radiotherapy, however, there are still lack of breakthrough therapy designation. Cancer immunotherapies hold great promise, where the mechanism of interaction between immune cell and tumor remains poorly understood. Understanding of immune cell infiltration in solid tumor plays an important role in cancer immunotherapy. This paper describes injection molded plastic chip to mimic complex three-dimensional tumor-vasculature for evaluating immune cell infiltration and their cytotoxicity. Our device facilities simple and high-throughput screening, constituting of 28 wells per device. Using our system, Co-culture conditions that both tumors and blood vessels were adequately benefited were established. Also, we characterized the aberrant vasculature according to the colorectal tumor subtypes and confirmed increased blood vessel the permeability, which is the major feature of aberrant tumor vasculature. Moreover, we evaluated Natural killer(NK) cell infiltration and cytotoxicity according CMS subtypes. NK cell showed higher cytotoxicity to CMS 1 type colorectal cancer compared to the other subtypes. This result confirmed that NK cell is the crucial effector in innate immune system as a first line of defense against pathogens. Therefore, we propose our plastic microfluidic chip as a high-throughput screening platform to evaluate lymphocyte cytotoxicity to various solid tumor including immune infiltration. Citation Format: Jiyoung Song, Hyeri Choi, Dohyun Park, James Yu, Nooli Jeon. High-throughput vascularized tumor array for In-vitro natural killer cell cytotoxicity testing [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO040.