According to WHO, around 10-25% of medical waste is declared dangerous. B3 waste is the residue of an activity containing hazardous substances that can endanger the environment, health and the survival of humans and other living things. The B3 waste must be neutralized before being discharged without further treatment. Activated charcoal (charcoal that has a wide surface area and large porosity after going through the activation process) is able to adsorb anions, cations, molecules in the form of organic and inorganic compounds so that they are used as adsorbents for low-grade pollutants in industrial products. The raw material for making activated charcoal can come from various wastes in the surrounding environment, for example corncobs and other porous materials. Therefore, the manufacture of activated charcoal from corn cobs can be a solution to the large amount of corn cobs waste that is thrown away. Making activated charcoal from corn cobs begins with coking with a retort at a temperature of 450˚C for 3 hours. After coking, the charcoal is activated chemically (soaking using sulfuric acid for 24 hours) and physically (reheating to the furnace at a temperature of 700˚C for 2 hours). Charcoal that has gone through the activation process is used as an adsorbent in hospital wastewater adsorption by the flow method. Samples were tested at BBTKLPP with standard parameters for wastewater quality (phenol, MBAS, TDS, TSS, ammonia, temperature, ph, COD and BOD) and heavy metals Cr, Pb, Cd. Based on the research that has been done, it can be concluded that the condition of the liquid waste of the PKU Gamping Hospital is not safe to be directly discharged into the river because the COD and BOD parameters are still above the maximum limit set by Perda DIY No. 7 th. 2016 Lampiran II concerning the quality standards for wastewater for hospital activities. Activated charcoal from corncobs and zeolite stones can neutralize hospital wastewater because it passes the wastewater quality standard test. From the test results obtained the best results are mostly at 0.5 L / minute discharge and at the 0th minute sampling. Metal content in hospital wastewater tends to be small.