Summary: Rectal suppositories constitute an industrially manufactured drug form as well as an element of pharmaceutical compounding. In medicine, substances of a various pharmacological profile are applied in the form of rectal suppositories. The representative group for this drug form and the route of administration are non-steroidal anti-inflammatory drugs (NSAIDs) and diclofenac is an example of the leading API (Active Pharmaceutical Ingredient). A form of a drug in which it is applied is of key significance for the effectiveness of the diclofenac therapy. It is necessary for the drug form to be compatible with the route of administration, therefore, diclofenac can be found in tablets, capsules, gels, suppositories, injections and others. The rectal route of drug administration is certainly not as popular as the oral route, additionally, its application is considered to be somewhat embarrassing and not very comfortable. Taking into account the biopharmaceutical advantages, it is an effective method for obtaining the optimal therapeutic effect. The effectiveness of suppositories clinical application depends on the properties of excipients forming the suppository base. The ability to melt or dissolve, rheological properties after liquefaction and mechanical strength in the solid state will determine the effectiveness of the therapy. The article presents the morphological and technological-pharmaceutical properties of rectal suppositories containing 100 mg of diclofenac sodium, commonly applied in pain treatment and inflammation of various aetiologies.