China's total imports from North Korea fell 13.4 percent in April from the previous month to $99.3 million.
China -- the North's sole major diplomatic ally and key trading partner -- has stopped buying coal from it, denying the regime access to a key source of the hard currency needed to fund its weapons programmes.
But the United States has been pushing China to do more.
China's total imports from North Korea fell 13.4 percent in April from the previous month to $99.3 million, the lowest since at least June 2014, Chinese customs data showed.
The total was nearly 44 percent below February's figure when Beijing's ban on North Korean coal came into force.
Chinese exports to the North fell 12 percent in April from the previous month to $288.2 million.
Tensions remain high on the Korean peninsula in the wake of Pyongyang's latest missile launch on Sunday.
The UN Security Council, backed by China, on Monday strongly condemned the test-firing. It instructed the UN sanctions committee to redouble efforts to implement a raft of tough measures adopted last year.
The United States has for weeks been negotiating a new Security Council sanctions resolution with China. But US ambassador Nikki Haley said last week that no final draft text had been clinched.
"On the basis of not violating the relevant (Security Council) resolutions, China maintains normal business and trade ties with the DPRK," foreign ministry spokeswoman Hua Chunying told reporters, using the initials of North Korea's official name.
"We are faithfully implementing the resolutions. We are not doing it as a gesture to another party -- we are just fulfilling our international obligations as a permanent member of the UN Security Council."
North Korea has carried out two atomic tests and dozens of missile launches since the beginning of last year in its quest to develop a missile capable of delivering a nuclear warhead to the continental United States.
The Security Council adopted two sanctions resolutions last year to ramp up pressure on Pyongyang as fears grow that Kim Jong-Un's regime is planning another nuclear test, which would be its sixth.
Under UN resolutions North Korea is barred from developing nuclear and ballistic missile technology.