Kumar drove to the house of former chief minister Rabri Devi at 10 Circular road to wish Lalu on his birthday.
Speaking to reporters, Nitish said, "Lalu Prasad has contributed immensely to Bihar politics and our society."
Meanwhile, stream of well-wishers comprising leaders, legislators, and party workers visited the 10 Circular road to extend their greetings.
Nitish Kumar also dedicated two road bridges over the river Ganga to the people of the state today.
At a function in the state capital attended among others by RJD supremo Lalu Prasad, Education Minister Ashok Chaudhary and a host of ministers and officials, Kumar dedicated the two bridges, Sonepur-Digha and Ara-Chapra, by pressing the button of remote control.
The two bridges will go a long way in improving road connectively between south and north Bihar and reduce vehicular traffic pressure on the dilapidated Gandhi Setu, the reconstruction of which is underway for sometimes.
The distance between various destinations between south and north Bihar too will be reduced drastically by more than 100 km.
The 5.25 km Sonepur-Digha rail-cum-road bridge was cleared by the UPA government in 2006 when Lalu Prasad was the Railway minister, while the 4.35 km four-lane Ara-Chapra bridge was given green signal by the Chief Minister in 2010.
Prime Minister Narendra Modi had dedicated to the nation the rail section of Sonepur-Digha bridge in March last but the road bridge could not be inaugurated then due to delay in construction of approach road on both Digha and Sonepur sides.
There will be restricted traffic on the two road bridges for the time being with the authorities deciding to allow movement of only small vehicles, according to officials.
Speaking on the occasion, the Chief Minister said that that he was happy to dedicate the two road bridges to the people of Bihar on a day when the RJD supremo Lalu Prasad is celebrating his 70th birth day.
Kumar said the railway authorities should have invited Lalu Prasad on inauguration of the rail section of the Sonepur-Digha rail-cum-road bridge last year as it was conceived during Prasad's stint as railway minister in 2006.
"Those who organised inauguration function for launch of rail bridge between Sonepur and Digha by the Prime Minister Narendra Modi last year did not have decency to invite Prasad," the Chief Minister said.
The Sonepur-Digha bridge was earlier meant for rail project only, but after becoming the railway minister in 2004 Lalu Prasad impressed upon the UPA government to incorporate road part of the bridge too to smoothen road connectivity between South and North Bihar, he recalled.
The Chief Minister said that his government has decided to honour Bihar's two great sons, Veer Kunwar Singh and Jai Prakash Narayan, popularly known as JP, by naming the Ara-Chapra bridge after the former ahead of 160th anniversary of celebrations of his participation in the 1857 rebellion against the British rulers.
The Sonepur-Digha bridge has been christened after JP, he said.