A resolution to this effect was passed at the party state council held here today.
Reacting to the development, UDF Chairman and Opposition leader Ramesh Chennithala termed JD(U) decision "political deceit".
Talking to reporters after the meeting, party president Veerendra Kumar, who resigned from the Rajya Sabha last month, said: "The decision to leave the UDF was a unanimous one".
Kumar said the JDU was of the view that the LDF was more effective in countering the "communal threat posed by the Sangh parivar under the BJP rule".
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Expressing gratitude to UDF leaders, Kumar said: "The UDF has not shown any ingratitude to us. The UDF had only gained with our party's association."
However, politically we suffered a lot, he added.
Hitting out at the BJP-led NDA government, he said under its rule, the private life of citizens had been lost.
They talk about nationalism and patriotism, but "are selling the nation to multi-nationals", he charged.
In these circumstances, the Left movemenmt has to be strengthened, he said.
Kumar also recalled the days he spent in jail along with Chief Minister and CPI-M veteran Pinarayi Vijayan during the emergency period.
The Veerendra Kumar-led state unit had broken away after party chief and Bihar Chief Minister Nitish Kumar joined the NDA.
Kumar had joined the Congress-led UDF after snapping ties with the LDF over differences with the CPI(M) on the Kozhikode Lok Sabha seat in 2009.
Terming the JD(U) decision "political deceit", Chennithala said it was the UDF that gave sanctuary and protection to the JD(U) when they were "kicked" out by the LDF.
Chennithala said it was the responsibility of Kumar to spell out the "losses suffered by the JD(U) after it joined the UDF".