The legislature is a unicameral body known as the Legislative Assembly. Its members are referred to as deputies (diputados). They are elected every three years according to a system of proportional representation. The assembly elected in March 1988 was composed of sixty deputies and sixty alternates (suplentes).

There is no restriction on the reelection of deputies. To serve in this capacity, however, one must be a Salvadoran by birth and over twenty-one years of age. Those prohibited from seeking election to the assembly include the president and vice president of the republic, government ministers and vice ministers, active-duty military personnel, and relatives of the president within the fourth level of consanguinity or the second level of affinity. Elected deputies, however, may serve as ministers or vice ministers, heads of official autonomous institutions, or chiefs of diplomatic missions. Such individuals do not participate in the business of the assembly but may be reintegrated into that body at the conclusion of their service in such a post.

The powers of the Legislative Assembly are considerable. It is the body that determines the statutory laws of El Salvador. It has the power to levy taxes, to ratify or reject treaties negotiated by the executive branch with foreign governments or international organizations, and to regulate the civil service. The assembly also wields the power of the purse as the body that approves the national budget in its final form. Perhaps just as important in a political sense is the assembly's power to place individuals, through a majority vote, in the following posts: president (chief justice) and magistrates of the Supreme Court, president of the Central Electoral Council, president and magistrates of an independent government auditing body known as the Court of Accounts (Corte de Cuentas), the attorney general, and the procurator general. By naming to these positions members of parties or factions opposed to the president, the Legislative Assembly can (and has, in some instances) impede the workings of government to a significant degree. The assembly also has the power to declare war, ratify peace treaties, and grant amnesty for political offenses or common crimes.

Legislation may be introduced not only by deputies but also by the president, by way of his ministers the Supreme Court, in the case of laws pertaining to the judiciary and local municipal councils, with regard to municipal taxation. A presidential veto of a law passed by the Legislative Assembly may be overridden by a two-thirds vote of that body. The executive may raise objections to a law on constitutional grounds in such a case, the Supreme Court serves as the arbiter. If a law submitted to the Supreme court by the president is ruled to be constitutional, the president is compelled to sign it into law.

Data as of November 1988