She said, "That incursion skirts important principles of federalism and therefore cannot be legitimate, in this court's view."
The judge said the law fails because it tries to re-examine states' decisions concerning same-sex marriage. She said such a sweeping review interferes with a system of government that places matters at the core of the domestic relations law exclusively within the province of the states.
The ruling came in a case brought by Edith Windsor, a woman whose partner died in 2009, two years after they married in Canada. Because of the federal law, Windsor didn't qualify for the unlimited marital deduction on her late spouse's estate and was required to pay $363,053 in federal estate tax. Windsor sued the government in November 2010.
As part of her ruling, Jones ordered the government to reimburse Windsor the money she had paid in estate tax.
The disparate treatment goes to equal protection under the law. Judge Jones' ruling came just days after the 1st Circuit found that DOMA was unconstitutional in denying federal benefits to same-sex couples. Two judges in the 9th Circuit have issued district court rulings along the same lines.