May's container traffic slumped to 2.1 million TEUs from 2.63 million TEUs recorded in May 2008, the data showed.
Compared to April's volume at 2.09 million TEUs, the increase was marginal.
Dominant operator PSA posted lower throughput of 2.04 million TEUs last month, down 19.4% compared to 2.53 million TEUs in the same period a year ago.
Month-on-month, PSA moved slightly higher throughput compared to 2.03 million TEUs in April.
Smaller port operator Jurong Port posted a sharp plunge in container throughput. Volumes plunged 44.7% to 52,000 TEUs in May 2009 from 94,000 TEUs in May 2008.
Jurong Port also handled less containers in May compared to 56,000 TEUs handled in April.
For the first five months this year, container movements were pegged at 9.93 million TEUs, down 18% from 12.11 million TEUs in the corresponding period last year.