Normal paper does not have antimicrobial properties. To impart antimicrobial properties to paper for medical applications, a guanidine-modified starch was prepared via two reaction steps using guanidine hydrochloride (GH) as a modifier, and added to the paper coating formula. FT-IR demonstrated that the GH was successfully grafted onto the starch via the Schiff base reaction. After coating with the modified starch, the antimicrobial performance of the paper against E. coli and S. aureus was evaluated by the disc diffusion method. The results indicated that the paper treated with the guanidine-modified starch exhibited excellent antimicrobial properties against the E. coli and S. aureus. In addition, the dry and wet strength indexes of the coated paper increased by 25% and 100%, respectively, as compared to the control paper.