Objective:To observe the relationship between autophagy regulation activity of chromosome 19 open reading frame 5 (C19ORF5) and malignant degree of colorectal cancer and chemosensitivity of paclitaxel.Methods:The tumor tissues and normal adjacent tissues of 141 colorectal cancer patients from 2015 to 2017 in the Second Affiliated Hospital of Harbin Medical University were selected. The expressions of C19ORF5 protein and mRNA were detected by immunohistochemistry and timed quantitative polymerase chain reaction. The correlation between C19ORF5 protein regulating autophagy activity and malignancy of colorectal cancer was analyzed. All 141 patients received postoperative chemotherapy, among whom 91 patients received conventional chemotherapy (capecitabine combined with oxaliplatin, conventional chemotherapy group), and 50 patients received conventional chemotherapy combined with paclitaxel (paclitaxel group). Six course of treatment was treated in both groups.Results:Autophagosomes could been seen under transmission electron microscopy. C19ORF5 protein was pale yellow to tan granules, and was expressed in the cytoplasm. The C19ORF5 protein staining intensity of cancer tissue was significantly stronger than that of normal tissue, and the staining intensity of stage Ⅱ was significantly higher than that of stage Ⅳ. The high expression rate of C19ORF5 protein in patients with stage Ⅰ to Ⅱ was significantly higher than that in patients with stage Ⅲ to Ⅳ: 83.3% (25/30) vs. 17.1% (19/111), and there was statistical difference ( P<0.01). The expression of C19ORF5 mRNA in cancer tissues was significantly higher than that in normal tissues: 1.17 ± 0.45 vs. 0.82 ± 0.29, and there was statistical difference ( P<0.05). The expression level of C19ORF5 protein in cancer tissue was related to tumor stage, carcinoembryonic antigen and liver metastasis ( P<0.01 or <0.05); the expression level of C19ORF5 protein in cancer tissue was not related to lymph node metastasis ( P>0.05). Of the 91 cases in conventional chemotherapy group, chemotherapy was effective in 70 cases (76.9%) and ineffective in 21 cases (23.1%). Of 50 cases in paclitaxel group, it was effective in 42 cases (84.0%) and ineffective in 8 cases (16.0%). There was no statistical difference in effective rate between 2 groups ( P>0.05). In conventional chemotherapy group, there was no significant difference in serum C19ORF5 protein expression levels between cancer tissues before and after chemotherapy in effective patients and ineffective patients ( P>0.05); there was no significant difference in serum C19ORF5 protein expression levels between effective patients and ineffective patients after chemotherapy ( P>0.05). In paclitaxel group, the expression level of C19ORF5 protein in cancer tissues before chemotherapy was significantly higher than that in serum C19ORF5 protein after chemotherapy: 0.9 ± 0.3 vs. 0.5 ± 0.2, the expression level of serum C19ORF5 protein in patients with effective chemotherapy was significantly lower than that in ineffective patients: 0.5 ± 0.2 vs. 0.8 ± 0.2, and there were statistical differences ( P<0.05). Conclusions:The high expression of C19ORF5 protein can increase the autophagy activity of colorectal cancer tissue; C19ORF5 protein regulates autophagy activity and is negatively correlated with the malignant degree of colorectal cancer; C19ORF5 protein may increase the sensitivity of paclitaxel chemotherapy by enhancing autophagy activity.