We experienced a case of alachlor herbicide (Lasso) intoxication. A 57-year-old man was transported to our hospital by ambulance after ingesting 450 mL of Lasso. He was unconscious and had difficulty in breathing. Gastric lavage was performed after tracheal intubation and the patient was placed on mechanical ventilation. Activated charcoal and laxative were administrated. Even after admission, disturbance of consciousness persisted. He had liver and kidney disorders but these did not progress to multiple organ failure. He experienced convulsions from day 4 and was administered anticonvulsants. Convulsion was intractable and needed long-term treatment. His general condition improved until discharge. He was weaned from mechanical ventilation and recovered consciousness, but he still displayed tremors. The herbicide (Lasso) is a combination of alachlor and monochlorobenzene. Studies have shown that alachlor is neurotoxic and monochlorobenzene accumulates in the brain. In case of intoxication with the herbicide Lasso, treatment is required for ameliorating neurotoxic effects and intractable convulsion as well as liver and kidney disorders, gastrointestinal mucosal damage, hematopoietic disorder, and acute circulatory failure.