Background and Objective: Cerebral palsy is a non-progressive impairment in immature brain which hemiplegic kind of it referred to more impairment in one side of the body. The aim of this study was to determine the effects of treatment environment on results of the modified constraint-induced movement therapy in children with hemiplegic cerebral palsy. Materials and Methods: In this single blinded, randomized controlled trial, hand function of 10 children with hemiplegic cerebral palsy in a simple random sampling of Ahvaz city was measured in 2 equal groups in 2010. Treatment protocol consists of constraint-induced movement therapy for 3-week by an occupational therapist in 2 environment (home and clinic). Measures were conducted pre and post and 1 month after the treatment period by Pediatrics Motor Activity Log and Bruininks-Oseretsky Test of Motor proficiency. Sample randomization and data analysis by analysis of variance with repeated measures were conducted by SPSS-16 software with alpha level set at 0.05.   Results: All subjects exhibited significant improvement (p < 0.05) in post treatment measures (speed and dexterity mean change: home group from 0.60±0.32 to 1.50±0.26 and clinic group from 0.52±0.38 to 1.52±0.24) except subtest upper limb coordination. At follow up, improvement in both groups sustained but home group exhibited significantly continued (p < 0.05) and higher improvement than clinic group (mean change from 1.50±0.26 to 2.10±0.16). Conclusion: Modified constraint-induced movement therapy appears to improve hand function. More improved performance in home group, places the practice in natural context as preference method for treatment of children with cerebral palsy.