To evaluate the cost- effectiveness of enzyme replacement therapy (ERT) in comparison with standard medical care without ERT in patients with type 1 Gaucher disease (GD-I) in Iran. The analysis is based on societal perspective. A markov state-transition model was built, in which different phases of GD were distinguished. The cycle length of this markov model represents 1 year of life. The health outcomes were estimated on Quality Adjusted Life Years (QALY) gained. The cost outcomes were the average direct costs associated with each state in both arm (relating to drugs and medications, monitoring, routine follow-up and adverse event management). The model was developed based on data from Iran Food and Drug Administration (IFDA) Gaucher registry, and was validated with literature data and expert opinion. All of the effectiveness parameters were derived from systematic review of the published literature. Over a 70-year lifetime, an untreated GD-I patient will generate 39.67 QALYs. Starting ERT in a symptomatic patient increases number of QALYs gained by 10.78. The average annual cost of ERT is ranged between 40,941.1$ and 69,176.5$ per patient. The lifetime cost of ERT, which starting from symptomatic, stage is3,477,710.8$ against 87,885.4$ without ERT; a difference of 3,389,825$. Consequently, the incremental cost-effectiveness ratio (ICER) was 45415$. The use of ERT is highly effective for GD-I with substantial health gains, but highly costly treatment. The threshold analysis showed that its ICER is almost 10 times higher than Iran gross domestic production, and thus is not cost effective.