Fatah secured 54% of the vote compared to Hamas's 26%.
Though the elections were mostly about local issues such as roads and water, Fatah's showing on Friday was in line with a recent modest rise in support for the party following Israel's pullout from the Gaza Strip.
Faced with early results showing a worse-than-expected outcome, the Hamas resistance group complained that many of its candidates were detained by Israeli troops before Thursday's election.
Local elections were held on Thursday in 104 West Bank towns and villages. It was the third of four rounds of municipal elections, with no date set yet for the final vote in the largest Palestinian cities.
The Local Elections Commission said final results showed Fatah with 54% and Hamas with 26%.
In the previous rounds, Hamas won 30% or more, and took control of some of the largest towns in the Palestinian territories, including Rafah, Bait Lahiya and Qalqiliyah.
Many had predicted a poor
showing for Fatah
Many had predicted a poor showing for Fatah, the ruling party for more than a decade. Its popularity has been waning because of widespread corruption, and many thought Hamas would get the "sympathy vote" amidst the Israeli offensive.
Yet Palestinian pollster Khalil Shikaki recently told The Associated Press that Fatah has begun to reverse its popularity fall following Israel's Gaza withdrawal, with many Palestinians preferring a return to diplomacy.
In local elections, Hamas's support is largely based on Palestinians' longing for clean government. Hamas's ideology of armed resistance has not been a major issue.
Results in local elections are not necessarily a clear reflection of the respective strengths of political parties, since many voters choose candidates according to clan membership, not party affiliation.
The biggest contest between Hamas and Fatah will come in parliament elections in January.
Palestinian peace negotiator Saeb Erekat, of Fatah, said Thursday's vote would not necessarily predict the outcome of the parliament election. "The issue of January elections cannot be isolated from the results today, but we can't say it will be an exact copy," he said.
"The issue of January elections cannot be isolated from the results today, but we can't say it will be an exact copy"
Palestinian peace negotiator
Sami Abu Zuhri, a Hamas spokesman in Gaza, said he did not trust the accuracy of preliminary results issued by the election commission, and that Hamas would soon publish its own count.
In previous rounds of municipal voting, Hamas and Fatah released different figures, in part by each claiming independent lists as affiliates.
Abu Zuhri also said Hamas suffered as a result of the recent Israeli arrest campaign in which more than 400 Palestinians, the bulk Hamas supporters, were rounded up this week.