Acting on a tip-off, the mini-truck was intercepted at Vyas colony in Bikaner and four tonnes of poppy husk packed in 100 bags were seized, a police official said.
Harendra Singh - kingpin of the smuggling gang - hailing from Punjab and five others including a minor boy, who were sitting in the mini-truck were arrested, he said.
Poppy-husk was being smuggled from Neemach in Madhya Pradesh to Punjab via Rajasthan, the official said.
A case under NDPS (Narcotic Drug and Psychotropic Substance Act) was registered against the accused, the official said.