you have to make the ester first and react it with hydrazine at RT or heating 

You can proceed by acid chloride followed by react it with hydrazine at RT

@Eugene Yang I am ready with methyl ester.But I performed reflux in ethanol. Reaction didn't proceed further.

If the ester is liquid, try dropwise addition followed by reflux of the Methyl ester directly with the Hydrazine monohydrate

someone asked a similar question before

https://www.researchgate.net/post/What_is_the_best_procedure_and_condition_to_prepare_hydrazide_by_reaction_of_ester_and_hydrazine

Other options 

http://pubs.acs.org/doi/abs/10.1021/jo026288n

http://www.sciencedirect.com/science/article/pii/S0040403900801975

http://www.arkat-usa.org/get-file/20032/

and apparently directly from aromatic carboxylic acids as well

http://www.heteroletters.org/issue24/pdf/paper-3.pdf

@Sid James Nelson Ester is a solid.

@Eugene Yang: Thank you for your valuable inputs.

You can firstly prepare the ethyl/methyl ester and reflux it in anhydrous ethanol/methanol in the presence of hydrazine (10Eq hydrazine/1Eq ester).

Time of reaction 10h

If a precipitate forms, filtration of the solid followed by recrystallization in ethanol will afford you the pure product

Regards