Serbia's parliamentary republic and its 250-seat single-chamber National Assembly
Background
The Council of Europe's Venice Commission records that Serbia is a parliamentary republic, with the government divided into legislative, executive, and judiciary branches. The country's parliament, the National Assembly, is a single chamber. Asked whether Serbia ever had a bicameral system, the Venice Commission's record answers "Always unicameralism", so the country has never worked with a second chamber. That single house has 250 seats. Serbia had one of the first modern constitutions in Europe, the 1835 Constitution, known as the Sretenje Constitution, and has since adopted 10 different constitutions. The current constitution was adopted in 2006. The European Committee of the Regions' division-of-powers profile describes the same arrangement: the Parliament (National Assembly) is unicameral, the Government is led by a Prime Minister and the Head of State is the President.
In plain words
Unicameral Single-chamber legislature — A legislature with only one house, so a bill is never sent on to a second chamber.
Venice Commission European Commission for Democracy through Law — The Council of Europe's advisory body on constitutional questions.