The Constitution of Laos is the communist state constitution of Laos. It specifies the functions and powers of the systems of state organs of the Lao People's Democratic Republic, and defines the rights and duties of citizens. The constitution was adopted on August 14, 1991, 16 years after the 1975 establishment of the Republic, a period during which the country functioned without a written constitution or published penal and criminal codes. The 1991 Constitution consisted of a Preamble and 80 Articles, and it legally established a set of authorities that resemble the traditional differentiation among executive, legislative, and judicial branches of government. Since the ratification of the 1991 Constitution, it has been amended three subsequent times in 2003, 2015 and 2025. The most recent series of amendments to the constitution were ratified on March 10th, 2025.

Laos' first constitution was drafted and adopted by the Lao Issara (Free Laos) government on October 12, 1945, containing 41 articles, with some of its articles inspired by the June 1932 provisional constitution of Thailand.

On August 14, 1991, 16 years after the establishment of the LPDR, the Supreme People's Assembly (SPA), the country's highest legislative organ, adopted a constitution. While the SPA had been charged with drafting a constitution in 1975, the task had lower priority. It was not until the Third Party Congress that party Secretary General Kaysone stated that the LPRP should "urgently undertake the major task...of preparing a socialist constitution at an early date."

Laotian press reports subsequently revealed that a constitutional drafting committee was working informally under the chairmanship of Politburo member Sisomphone Lovansai, a specialist in party organization, with the help of East German advisers. On May 22, 1984, the SPA Standing Committee formalize the appointment of Sisomphone to head a 15-person drafting committee.

The political institutions had functioned without a written constitution for 15 years. International development agencies were reluctant to invest in Laos given the absence of a fixed, knowable law. Amnesty International, in a 1985 report on Laos, asserted that without a constitution or published penal and criminal codes, citizens were "effectively denied proper legal guarantees of their internationally recognized human rights." The party newspaper, Xieng Pasason (Voice of the People), commenting in June 1990 on the absence of a constitution and a general body of laws, acknowledged that "having no laws is... a source of injustice and violation, thus leading to a breakdown of social order and peace, the breeding of anarchy, and the lack of democracy."

According to some reports, progress in Laos had been blocked by differences within the Politburo over certain substantive clauses. The party leadership, accustomed to rule without question, may have assigned a low priority to producing a document that might eventually lead to challenging their authority.

After the new SPA was elected in March 1989, it formally appointed a 17-member constitutional drafting committee. The National Radio of Laos reported that the drafting committee was working "under the close supervision of the Political Bureau and the Secretariat of the Party Central Committee." 6 members of the drafting committee were members of the Central Committee; 2 of these members served on the SPA, which had 6 members on the drafting committee.

In April 1990, after securing approval of its document from the LPRP Politburo and the Secretariat, the SPA made public the draft constitution. With its publication, the party Central Committee issued Directive Number 21, on April 30, 1990, calling for discussion of the draft, first among party and government officials and then among the public. The discussions, while orchestrated by party cadres, did not always please party authorities. An LPRP spokesman released a memo complaining that "people in many major towns" had dwelled too much on what the constitution had to say about the organization of the state.