Heat stress has been implicated to have adverse effect on the performance of livestock and addition of betaine to their diets has been reported to mitigate this negative impact. This study investigated the haematological and serum biochemical parameters of broilers fed different levels of betaine during dry season using 180 1day-old broiler chicks which were randomly assigned to five treatments (with 36 birds per treatment). Each treatment was replicated thrice (with 12 birds per replicate) in a completely randomized design. Treatment 1 was the control (without betaine) while treatments 2, 3, 4 and 5 contained 1, 2, 3, and 4g of betaine/kg of feed, respectively in an experiment that lasted for 56 days. At the end of the feeding experiment, blood samples were collected from the birds for haematological and serum biochemical analyses. Results revealed that haematological parameters were not significantly affected by the levels of dietary betaine, except platelet which increased significantly (p<0.05) with increasing levels of betaine. Serum albumin concentration was significantly higher (p<0.05) in broilers on diet 3 (1.55g/dl) compared with broilers on other diets. Serum thyroxine concentration increased significantly while corticosterone concentration decreased significantly with increasing levels of betaine. Serum enzymes were not significantly affected by the treatments. Serum electrolytes were significantly reduced (p<0.05) in broilers fed dietary betaine, although, they were within the normal ranges for broilers. This study revealed that betaine can be incorporated into the diets of broilers up to 2g/kg of diets to reduce heat stress without adverse effect on the health status of the birds.