The purpose of this study is to investigate the psychometric properties (validity and reliability) and standardization of the Adaptive Behavior - Scale (AAMR, ABS, S:2)- part One in Muscat governorate. This will provide psychologists and professional with a suitable instrument to measure adaptive behavior when diagnosing individuals with intellectual disabilities. Adaptive Behavior Scale was administered to a sample of (272) students (136= n students with Intellecual disabilities, n= 136 of normal students) and both groups is aged between 8- 13 years old. To estimate the validity of the scale the study used three methods: face validity, criteria- related validity and discrimination validity. To estimate criteria- related validity, the correlation was calculated between the scale and Raven Coloured Progressive Matrices, results showed a statistically significant positive correlation of (r=0.65, p< 0.05). The results showed that the AAMR, ABS was able to differentiate between two groups (students with intellectual disabilities and normal students), and between different age categories. Reliability was estimated by test- retest reliability and internal consistency" Cronbach Alpha". The results showed that the scale has acceptable level of consistency, and stability overtime. Having established the required psychometrics properties of the scale, the performance norms were derived using percentile ranks because of their ease, clarity, and ability to determine the location of the individual relative to standard group. The norms were derived for the sample (n= 272), and the two groups: students with intellectual disabilities (n=136) and normal students (n= 136) separately, for both male .and female combined. Finally a number of recommendations and suggestions have been introduced