Abstract: Accumulation of ammonia is toxic and can cause stress in cultured animals leading to immune depression and increase susceptibility to diseases in aquaculture systems. The present study was aimed to quantify stress in shrimp exposed to different levels of total ammonia nitrogen, TAN, (8.1, 3.8 and 1.1 mg L-1) for 10 days and subsequently infect with White Spot Syndrome Virus (WSSV) by feeding positive WSSV shrimp. Haemo-chemicals alanine transaminase (ALT), aspartate transaminase (AST), total protein (TP), glucose and electrolytes (Na+, Cl¯, K+) were measured to quantify the stress caused by ammonia and WSSV infection. Shrimp exposed to 8.1 mg L-1 TAN for 10 days revealed significantly high haemolymph ALT, AST and TP while shrimp exposed to 3.8 mg L-1 TAN showed significantly low TP. These changes in haemolymph parameters showed that exposure to 3.8 mg L-1 TAN for 48 h was sufficient to stress the shrimp. Stress in shrimp exposed to ammonia for 10 days further increased significantly when shrimp were infected with WSSV. During post WSSV infection, haeomolymph TP significantly decreased with increase in TAN 1.1, 3.8 and 8.1 mg L-1 treatments. Therefore, exposure of shrimp to higher ammonia level had stressed the shrimp more and the stress further increased by subsequent infection with WSSV as illustrated by changes of haemo-chemical parameters.