Shanghai YTO Express said it took responsibility for the deliveries, which left one unwitting recipient dead and caused seven other people to fall ill.
The company said its employees had performed routine inspections of the deliveries, which took place last month in Shandong Province.
The toxic chemical turned out to be methyl fluroacetate and apparently leaked on to the other parcels during shipment, China's Xinhua news agency said.
Xinhua said delivery services have been booming in China, which has led to concerns about lax supervision and poor service.
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