In 1990 he was elected President of the Chișinău City Council and deputy in the first democratic parliament (1990-1994) of the
Republic of Moldova. During the period 1990-1994 he was
mayor of Chișinău, during which he manifested himself as the leader of the
Popular Front of Moldova. Nicolae Costin was the co-author the
Declaration of Independence of the
Republic of Moldova (27 August 1991). He supported the problems of the
Romanian language and the return to the
Latin script, participating in the elaboration of the law on the state language. He is considered the first mayor of Chișinău municipality who promoted more reforms in the development of the capital. On his proposal, the streets of
Chișinău have received national names (
Traian,
Ștefan cel Mare,
Nicolae Milescu-Spataru,
Mihai Eminescu,
Ion Creangă,
Metropolitan Bănulescu-Bodoni,
București, Calea Ieşilor, etc.), causing the dissatisfaction of anti-Romanian political organizations, which have demanded, in every electoral campaign, to return to the old Soviet names of the streets of Chișinău. Nicolae Costin contributed, together with the ministries of the Republic of Moldova, to the opening of the high schools, as follows: Romanian-English
"Mircea Eliade", Romanian-Italian
"Dante Alighieri", Romanian-French
"Gheorghe Asache" and Romanian-German
"Mihail Kogălniceanu", libraries, including the
"Onisifor Ghibu" Library, at the reopening of the churches, including the
Cathedral in the center of Chișinău, at the restoration of the monument of
Stephen the Great from
Chișinău. The busts of the classics of the Romanian language were installed and uncovered on the
Alley of Classics from the
"Ștefan cel Mare" Central Park. == Honours ==