The present invention relates to a mesalamine rectal suppository designed to provide improved comfort of use. One embodiment of the invention is a mesalamine rectal suppository containing mesalamine and one or more pharmaceutically acceptable excipients, wherein the drug load of the suppository ranges from 35% to 50%. Another embodiment of the invention is a mesalamine rectal suppository containing from about 850 to about 1150 mg mesalamine and one or more pharmaceutically acceptable excipients, wherein the total weight of the suppository ranges from about 2250 to about 2700 mg. Yet another embodiment of the invention is a mesalamine rectal suppository comprising mesalamine having a tap density ranging from about 600 to about 800 g/L (as measured by USP <616>) and a hard fat having an ascending melting point of 32 to 35.5.degree. C. Methods of preparing and methods of treatment with mesalamine suppositories are also provided. The invention further provides a method of determining a dissolution parameter (such as dissolution rate) of a mesalamine rectal suppository, such as a 1 g mesalamine suppository, by measuring its dissolution with USP Apparatus #2 at 40.degree. C. and a paddle rotation speed of 125 rpm in 0.2 M phosphate buffer at a pH of 7.5.