Objective: One of the challenges in gene therapy is the transfer of the gene to the target cell. MicroRNAs (miRNAs) regulate gene expression after transcription by binding directly to the messenger and play a vital role in cell behaviors and the pathogenesis of some diseases. This study was aimed at developing poly (lactic-co-glycolic acid) (PLGA)-based nanoparticles (NPs) for gene delivery to endometriotic cyst stromal cells (ECSCs). Materials and Methods: In this experimental study, endometriosis cells were isolated from women with severe endometriosis (DIE) and digested by the enzymatic method (40 μ, g/ml DNAase I and 300 μ, g/ml collagenase type 3). PLGA-based NPs were synthesized and characterized. The size of sole PLGA NPs and PLGA/miRNA were 60 ±,4 nm and 70 ±,5. 1 nm respectively. Poly lactic-co-glycolic-based NPs were used as vector carriers for miRNA 503 transfection in endometriosis cells. The cells were divided into the five groups of control and four doses (25, 50, 75, and 100 μ, m) of miRNA 503/PLGA at 12, 24, 48, and 72 hours. Viability and apoptosis were evaluated by the MTT assay and Annexin Kits. Data were analyzed by one-way analysis of variance. Results: The results show that the size of PLGA/miRNA complex with dynamic light scattering (DLS) was 70 ±,5. 1 nm and zeta potential values of the PLGA/PEI/miRNA complexes were 27. 9 mV. Based on the MTT assay results, the optimal dose of miRNA 503/PLGA was 75 μ, m, at which the viability of ECSCs was 52. 6% ±,1. 2 (P≤, 0. 001), and the optimal time was 48 hours. The apoptotic rates of ECSCs treated with PLGA/miRNA503 (34. 75 ±,4. 9%) were significantly higher than those of ECSCs treated with PLGA alone (3. 35 ±,2. 58%, P≤, 0. 01). Conclusion: Cell death increased with increasing the concentration of miRNA,thus, it can be suggested as a treatment for endometriosis.