Objective To research the expression of ARL family and its correlation with prognosis in stomach adenocarcinoma. Methods The gene expression and mRNA levels of ARL family in gastric cancer were extracted from TCGA database, GTEx project, MSK cancer gene detection and so on; the relative and differential expression were analyzed using various databases above. Immunohistochemistry (IHC) was used to detect the protein expression of ARL9 and p53 in stomach adenocarcinoma. The clinical stage of gastric cancer from TCGA database and GTEx project was used to estimate the correlation between ARL family and clinical stage. The data of overall survival (OS) from GEO, EGA and TCGA database were analyzed to assess the correlation between ARL family and OS. The samples of stomach adenocarcinoma were used to detect the mutation of ARL family and the corresponding prognosis. The GeneOntology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to determine the co-expression and pathways of ARL family. Results The mRNAs levels of ARL1, ARL4A, ARL4C, ARL5A, ARL5B, ARL8A, ARL9, ARL11, ARL13A, ARL13B, ARL15, ARL16 and ARL18 were significantly increased in gastric cancer tissues; the mRNA levels of ARL4D was significantly decreased（P＜0.05）. The IHC results showed that the protein expression of ARL9 and p53 was positive in gastric cancer tissues. The expression of ARL2 and ARL14 were closely related to clinical stages（P＜0.05）. Higher mRNA expressions of ARL2, ARL3, ARL4D, ARL9, ARL13B, ARL16 and ARL18 mRNA were discovered to be negatively associated with OS in stomach adenocarcinoma, higher mRNA expressions ofARL1, ARL4A, ARL14 and ARL15 were positively associated with OS. The mutation of missense, splice, truncating, amplification and deep deletion was detected in stomach adenocarcinoma. The GO and KEGG analysis showed the co-expression of ARL family and participation in the cell signaling. Conclusion ARL family is significantly expressed in gastric cancer and expressively associated with prognosis