Background: The aphasia screening test detects language and speech impairments, clarifying individuals’ language and speech abilities before administering a standardized aphasia diagnosis test. Objective: This study aimed to develop and validate an aphasia screening test for suspected cerebrovascular accident (CVA) patients with communication difficulties. Materials and methods: The study underwent two phases: developing and assessing psychometric properties. Five experts established content validity across receptive language, expressive language, reading, and writing. The Chiang Mai Aphasia Screening Test (CMAST) was evaluated on 14 CVA patients with and 14 without aphasia. Results: The content validity showed item-objective congruence ranging from 0.80 to 1.00. Sensitivity and specificity were 96.30% and 69%, respectively, with a maximum Youden’s Index at 65.30% and a cut-off point of 43 points. Concurrent validity was high (phi coefficient =0.67), and significant score differences (p<0.001) in construct validity confirmed the tool’s ability to distinguish aphasic from non-aphasic patients. Inter-rater reliability (ICC=0.99) and internal consistency (Cronbach’s alpha =0.97, 95% CI 0.95-0.98) were observed. Conclusion: The CMAST, comprising 45 items, exhibits sufficient validity and reliability for screening individuals suspected of aphasia due to CVA.