¹Laboratoire de Recherches Santé et Productions Animales, Ecole Nationale Supérieure Vétérinaire, Alger, ALGERIE DOI : 10.9775/kvfd.2017.17663 This study was conducted to determine the effect of dietary supplementation with cumin (Cuminum cyminum L.) seeds on growth performances, relative weights of carcass and viscera, haematological and biochemical parameters, and thyroid hormones concentrations of broiler chickens subjected to natural fluctuation of Algerian summer ambient temperatures. A total of 440 28-day old chickens were divided into 2 groups (5 replicates of 44 birds) with similar body weight (971±48 g): a "Control" group fed with a standard diet and a "Cumin" group receiving a basal diet supplemented with 0.2% of cumin. As a result of this study, dietary cumin supplementation did not significantly modify the growth rate and final body weights of heat-exposed chickens but it slightly improved feed conversion ratio (-7%, P=0.1). Carcass traits, viscera (liver, heart, gizzard, spleen, bursa and thymus) intestine morphology and abdominal fat of heat stressed birds did not reveal any changes by cumin inclusion compared to the control ones. Also, thyroid hormones (T3 and T4) concentrations were not significantly influenced by dietary cumin (P>0.05). However, heat-exposed chickens supplemented with cumin exhibited a significant (P<0.01) lower values of plasma glucose, cholesterol, triglycerides and total proteins and higher calcium concentrations than those of control group. Cumin dietary may be a successful means to enhancing diet conversion and reducing glaecimic, lipidaemic and calcaemic disorders in chronicallyheat exposed chickens. Keywords : Blood parameters, Broilers, Carcass, Chronic heat stress, Climate, Cuminum cyminum, Performance, Thyroid hormones