Haemobartonellosis is a disease caused by Mycoplasma haemofelis, previously called Haemobartonella felis, causing lethargy, fever, pale mucosa, and anemia of varying severity in cats. M. haemofelis is a small, gram-negative bacterium without cell walls that lives on the edge or surface (epicellular) of erythrocytes. The animal used as a case report is a domestic short-haired cat, ± 9 months old, an unsterilized female with a body weight of 3.3 kg. The results of the clinical examination and praesens status showed that the case cat experienced vomiting, loss of appetite, lethargy, mild ectoparasite infestation, pale mucosa, a CRT of more than two seconds, and increased respiratory frequency and body temperature. Routine hematological examination on the first day showed normochromic normocytic anemia, leukopenia, neutropenia, monocytopenia, and thrombocytopenia. Blood biochemical examination on the first day showed hypophosphatemia, hyponatremia, and hyperglycemia. A blood smear examination shows a round or ring-shaped formation on the edge or surface of the erythrocytes, which is morphologically identified as M. haemofelis. Based on the history, physical examination, and supporting examinations, the case cat was diagnosed as having haemobartonellosis. The case cat was treated for five days, and then on the sixth day, the case cat was sent home and underwent outpatient therapy because it showed an improving condition. Causative therapy for M. haemofelis is given oxytetracycline antibiotics for five days, followed by doxycycline antibiotics for 28 days during outpatient therapy. Frontline Plus® antiparasitic is given once to treat ectoparasites. The symptomatic therapy given is tolfenamic acid, once administered. The supportive therapy given is Lactate Ringer's infusion fluid therapy for 5 days and multivitamin, mineral, and hematopoietic supplements, namely Hematodin® by injection for five days, followed by Caviplex Syrup® for 28 days. Therapy for vulnus morsum is enrofloxacin for 8 days. After 28 days of outpatient therapy, the case cat showed clinical improvement and was actively playing.