This research was conducted at a company operating in the construction sector in Cikarang. The researcher conducted direct research on the welding process. The main process of focus in this research is on welding quality defects of the Slag Inclusion type. After knowing the main problem that is the cause of a defect, then carry out an improvement plan using the Root Cause Analysis (RCA) method, which is a method of repairing causal factors by analyzing what, how, and why a factor that causes a defect can occur with the aim of finding the root cause so that There needs to be changes to avoid errors. The RCA method has 2 approaches, namely the Fishbone diagram and 5 whys. Therefore, the author took the title "Increasing the Productivity of the Welding Process in the H-beam Production Line Using the RCA (Root Cause Analysis) Approach at Pt. XYZ” Root Cause Analysis (RCA) is a tool designed to understand the root cause of an event's problems based on causality in a process. The main factor that causes defects is humans who are careless when working, who do not see or observe the material when they want to start work or even underestimate the work. So implementing SOPs is very necessary to regulate workers so they don't work as they please, and outdated machines can hamper production and improve the quality of main raw materials.