Background: PAK (P21 activated kinase) is a family of serine threonine kinases, that consist of 6 members, PAKs 1-6, which are positioned at an intersection of multiple signaling pathways implicated in oncogenesis. Recent studies have found relationship between mutations of some PAK family genes and antitumor immunity. Here, we explored the associations of PAK family gene mutations with ICI response based on multidimensional data from multiple solid tumors. Methods: An immunotherapy cohort (Broad/Dana-Farber, Nat Genet 2018, N = 249) within 7 types of tumors as discovery stage, was used to explore the association of PAK family genes mutations with tumor mutation burden (TMB) and efficacy of immunotherapy. To further validate the predictive value of PAK family genes, we employed another ICI-treated cohort, MSKCC cohort (Samstein, Nat Genet 2019, n = 1661), as a validation cohort. TMB was calculated as the total count of nonsynonymous mutations in coding sequence. Results: In discovery cohort, compared to that in the PAK-Wt group, longer OS was observed in the PAK-Mut group (mOS: 31.3 vs 15.4 months, HR = 0.59, 95% CI: 0.36 to 0.96, P= 0.03). In addition, PAK-Mut group had higher TMB (P< 0.001). Median TMB in PAK-Mut group and PAK-Wt group is 17.79 (IQR, 7.45-36.55) Mut/Mb and 5.47 (IQR, 2.46-9.09) Mut/Mb, separately. In validation cohort, PAK-Mut patients also achieved significant improved OS compared with PAK-Wt patients (mOS: 44.0 vs 17.0 months, HR = 0.51, 95% CI: 0.37 to 0.69, P< 0.001). Moreover, multivariable analysis of validation cohort demonstrated that PAK-Mut was associated with better OS (HR = 0.71; 95%CI, 0.52-0.98; P = 0.036), after adjusting for Age, Gender, Metastasis, Treatment, TMB, Cancer type. Compared with PAK-Wt group (median [IQR]: 5.90 [2.95-10.04]), PAK-Mut group (median [IQR]: 21.19 [11.81-43.29]) also had higher TMB (P< 0.001). Conclusions: The results indicated that PAK family genes mutation was associated with a higher TMB both discovery and validation cohort. Analysis of discover and validation immunotherapy cohort data showed PAK family was associated with better OS. These findings indicate that these genes mutation may serve as a potential predictive biomarker for ICI in solid tumor patients.