Autism is a complex neurodevelopmental disorder without an unclear etiology. The diagnosis of autism is primarily based on behavioral performance scoring, which is subjective and susceptible to misdiagnosis and missed diagnoses. Currently, there are no biomarkers that can be applied to the clinical diagnosis of autism, and there is an urgent need to study objective and reliable molecular biomarkers. In this chapter, urine samples from children with autism and healthy controls at different ages (2–4, 3–7, and 10–15 years) were analyzed to identify potential biomarkers of autism. The findings indicated that urinary proteins may serve as promising early biomarkers for autism diagnosis.