Salah satu cara untuk melakukan efisiensi, meningkatkan mutu pelayanan dan meningkatkan keselamatan pasien di Amerika dengan menggunakan konsep Lean Thinking yang diterapkan di rumah sakit menjadi Lean Hospital. Di Rumah Sakit Atma Jaya yang merupakan Rumah Sakit Swata Kelas B Pendidikan, penelitian ini menganalisis alur pelayanan resep di Instalasi Farmasi Rawat Jalan sebagai data untuk perbaikan. Dengan menggunakan Root Cause Analysis (RCA), metodologi penelitian operational research, dilakukan observasi dan wawancara mendalam memperlihatkan bahwa kegiatan non value added bisa sampai 85% dan kegiatan value added hanya 15% pada penyiapan obat non racikan. Sedangkan untuk obat racikan kegiatan non value added sekitar 68% dan value added sebesar 32% nilainya. Data tersebut menunjukan bahwa telah terjadi pemborosan (waste). Usulan perbaikan untuk mengurangi pemborosan antara lain penggantian SIM RS yang baru dan menggiatkan fungsi Tim Kendali Mutu di Instalasi Farmasi. Bila perbaikan ini telah di implementasi, diharapakan terjadi peningkatan efisiensi di Instalasi Farmasi Rawat Jalan dan meningkatkan kepuasan pasien. Kata kunci: Konsep Lean, Lean Thinking, Lean Hospital, Resep, waktu tunggu obat, rawat jalan, pemborosan, analisis akar masalah One option to increase efficiency, service quality and patient safety in the United States of America is by using the Lean Thinking concept, which are implemented in Hospitals to become a Lean Hospital. In Atma Jaya Hospital, a class B study private hospital, the research analyses the workflow of prescription sevice in outpatient pharmacy departement to act as data for improvement analysis. Also, by utilizing Root Cause Analysis (RCA), operational research methology, indepth observation and interviews are conducted at compounding and noncompounding medicine storage of Outpatient Patient Departement, the result shows non-value added activities reaches 85%, while value added activities are only 15% on non-compounding medicine storage. While, on compounding medicine storage, non-value added and value added activities are at 68% and 32% respectively. These data clearly shows that great inefficiencies has occurred. Solution is suggested to increase the efficiency in the department, changing Hospital Information System and activate the Quality Control Team function. If these steps are implemented, we can expect the overall efficiency in the Outpatient Pharmacy Departement to improve significantly and resulted in higher patient satisfaction. Keywords: Concepts Lean, Lean Thinking, Lean Hospital, Prescription, drug waiting time, outpatient, waste, Root Cause Analysis