Kaiser attributed the marked slide in support among Democrats to a "post-presidential election fade." In November, 72 percent of that group expressed support for the law, compared with 57 percent who feel favorably toward it now.
Unaffiliated voters saw a similar but less dramatic decline in support, with 32 percent approving of the healthcare law compared with 37 percent in November.
"It's difficult to say whether this downward drop will last," Kaiser analysts wrote of the decline in overall support for the law. "Support seems to have shifted to the no-opinion category, up to nearly a quarter, a new high in Kaiser polling."
Obama's win in November cements the future of the Affordable Care Act. Implementation has begun in earnest in anticipation of 2014, when several major provisions will take effect.
Wednesday's poll was Kaiser's first effort since November to survey opinions on healthcare reform.