"What they had done to pass the state of emergency is fraud and we reject it," Abdul Razaq al-Hajri of the powerful Islamist opposition Al-Islah (Reform) party told AFP.
Parliamentary officials said more than 160 MPs out of 164 who attended a special session voted for the step, which the president announced on Friday, hours after regime loyalists gunned down 52 protesters near the university.
But Hajri said the turnout figure was fudged and that only 133 members attended. To take effect, the bill needed the approval of a majority in parliament and a quorum of more than 50 percent to validate the vote.
The parliamentary opposition, independent MPs and members of embattled Saleh's own General People's Congress who have resigned boycotted the session of Yemen's 301-seat parliament.
Before the vote, the two-month-old protest movement warned of dire consequences.
"A vote in favour is equivalent to approving the massacre of the innocent," demonstrators camped at a square near Sanaa University since February 21 said in an appeal to the deputies.
Saleh has ruled for more than three decades but now faces an escalating campaign for his removal.
The opposition has turned down an offer from Saleh to step down early, after he earlier insisted on holding office until his current term as president ends in September and not to run again.
On Wednesday, the offer was formalised in a document received by the opposition camp, its spokesman, Mohammed Gahtan, told AFP.
The proposal is for the formation of a unity government, a new electoral law with voting based on proportional representation, a referendum on a new constitution, and a legislative election.
The poll would be followed by the nomination by the end of 2011 of a successor to Saleh by the newly elected MPs, rather than next January.
On a visit to Cairo, US Defence Secretary Robert Gates, whose country lost another ally when Egyptian president Hosni Mubarak was ousted in February, said on Wednesday that it was too early to call an outcome in Yemen.
"I think things are evidently very unsettled in Yemen," Gates, who on Tuesday voiced concern that instability could boost the presence of Al-Qaeda in Yemen, told reporters. "It's too soon to call an outcome."
In contrast, French Foreign Minister Alain Juppe said on Monday that Saleh was facing an "unavoidable" exit from power.
The Russian foreign ministry in a statement urged all of its citizens to immediately leave Yemen, saying the situation showed an "escalating trend" that could only be resolved through dialogue.
Saleh's regime has been hit by a wave of defections in the ranks of the military, among influential tribal chiefs, Muslim clerics and senior diplomats as well as within Saleh's party, especially since Friday's massacre.
Late on Tuesday, the president invited Yemen's youths spearheading the protests to take part in an "open, truthful and transparent dialogue away from narrow partisan interests, prioritising the country's interests."
Saleh said he "sympathises" with the youths' demands and their "legitimate aspirations," the state news agency Saba reported, quoting an official in the president's office.
The demonstrators, for whom the impact of the state of emergency vote on their vigil outside the university was not immediately clear, have called for fresh demonstrations after Muslim weekly prayers on Friday.
Some of them have proposed a march on the presidential palace, although such attempts in the past have resulted in bloodshed, a correspondent at their camp said.
While elements of the regular army, which has tanks posted around key installations in Sanaa, have vowed to protect the demonstrators, the elite Republican Guard loyal to Saleh has deployed tanks around the palace.