Psyllium is a soluble fiber of low fermentability generally used in the prevention or treatment of constipation, causing increase fecal volume and quality. The constipation is defined as infrequent defecation, with extremely dry or hard feces, usually in association with tenesmus. Conditions that predispose dogs to constipation include perianal hernias, pelvic or lower back fractures, prostatic disease, and rectal neoplasias. Two experiments were conducted to evaluate the effects of psyllium in canines. The first evaluated a diet supplementation with 0%, 2% and 4% (as-fed basis) of ground psyllium seeds to dog diets. Eight adult healthy Beagle dogs were used. They received the diets during four days. A linear increase of faecal moisture was verified with the addition of psyllium (R2=0.54; p=0.0012), with no modifications in the faecal score or number of defecation per day. The second experiment included the evaluation of 24 dogs that received a diet supplemented with 2% of psyllium (as-fed basis) as part of the treatment of diseases that caused or predisposed to constipation. Among those canines, 11 (42.3%) presented perianal hernia as the main cause of dyschezia, 5 (19.2%), pelvic fracture, 2 (7.7%), spine diseases and other 6 dogs (23.1%) prostatic disease, inguinal hernia, inflammatory polyps in the rectum, anal glands inflammation, rectal neoplasia and myiasis in anal region. All dogs consumed the food and supplement properly, with no alimentary refusion, emesis or diarrhea episodes. Owners were invited to fill out a structured questionnaire. Nineteen (79.2%) reported that their dog had an easier defecation process (13 (51%) reported an expressive improvement), and 22 (91.7%) reported that dogs' feces turned from dry to normal or pasty. Overall, the owners' perception of faeces improvement was great noticeable with the psyllium supplementation, confirming the results of improving faecal moisture observed in the Experiment 1. These results reinforces the laxative effects of psyllium already reported in human medicine, indicating the use of this fiber in the clinical management of constipation.