Toxoplasmosis is a zoonotic disease caused by the parasite Toxoplasma gondii. Humans and animals can become infected by ingesting either tissue cysts containing T. gondii bradyzoites, from raw or undercooked meat, or sporulated oocysts from environmental sources. T. gondii oocysts are released in the faeces of cats and other felids, which are the parasite's definitive hosts (DH), leading to environmental contamination (Jones & Dubey, 2012). Therefore, vaccination of the feline host against T. gondii is an interesting strategy to interrupt the parasitic life cycle and subsequently limit contamination of intermediate hosts (IH). Objectives : Assess immunogenicity and protection of an attenuated live strain of T. gondii deleted for the Mic1 and Mic3 genes (Mic1-3KO) in cats, that was previously shown to be an efficient vaccine candidate in mouse and sheep models (Ismael, et al., 2006 ; Mévélec, et al., 2010). Methods : Cats were vaccinated with the Mic1-3KO strain subcutaneously in a first trial. Serum T. gondii specific antibodies were quantified by ELISA, and protection conferred by the vaccine candidate was assessed after challenge with a wild-type strain of T.gondii by following fecal oocyst excretion. As the natural route of infection by T.gondii is mainly foodborne, we developed a gastro-resistant formula to administer the vaccine candidate orally to cats in a second trial. The protocol included monitoring of T. gondii specific antibodies in the serum and oocyst excretion, as for the subcutaneous vaccination trial. Results : Subcutaneous or oral vaccination routes induced high specific antibody titers in cat sera, indicating that the Mic1-3KO strain is immunogenic for cats. As T. gondii antibodies are believed to be protective against a second infection in IH, we examined oocyst shedding by vaccinated cats, after oral challenge with a T. gondii wild-type strain. Surprisingly, a high antibody titer did not prevent cats from shedding oocysts from the challenge strain, regardless of the vaccination route. Conclusions : Our results show that the Mic1-3KO vaccine candidate is immunogenic in the feline host, is well tolerated and safe, but does not confer protection against oocyst shedding after natural infection with wild type T. gondii. This result highlights the particular relationship between T. gondii and its unique DH, which indicates the need for further investigation to improve vaccination strategies to limit environmental and livestock contaminations.