IMO currently has 174 Member States and three Associate Members
| Albania | 1993 |
| Lithuania | 1995 |
| Algeria | 1963 |
| Luxembourg | 1991 |
| Angola | 1977 | | Madagascar
| 1961 |
| Antigua and Barbuda | 1986 | | Malawi | 1989 |
| Argentina | 1953 | | Malaysia | 1971 |
| Armenia | 2018 | | Maldives | 1967 |
| Australia | 1952 |
| Malta | 1966 |
Austria
| 1975 | | Marshall Islands | 1998 |
| Azerbaijan | 1995 | | Mauritania | 1961 |
| Bahamas | 1976 | | Mauritius | 1978 |
| Bahrain | 1976 | | Mexico | 1954 |
| Bangladesh | 1976 | | Monaco | 1989 |
| Barbados | 1970 | | Mongolia | 1996 |
| Belarus | 2016 | | Montenegro | 2006 |
| Belgium | 1951 | | Morocco | 1962 |
| Belize | 1990 | | Mozambique | 1979 |
| Benin | 1980 | | Myanmar | 1951 |
| Bolivia (Plurinational State of) | 1987 | | Namibia | 1994 |
| Bosnia and Herzegovina | 1993 | | Nauru | 2018 |
| Brazil | 1963 | | Nepal | 1979 |
| Brunei Darussalam | 1984 | | Netherlands | 1949 |
| Bulgaria | 1960 | | New Zealand | 1960 |
| Cabo Verde | 1976 | | Nicaragua | 1982 |
| Cambodia | 1961 | | Nigeria | 1962 |
| Cameroon | 1961 | | North Macedonia | 1993 |
| Canada | 1948 | | Norway | 1958 |
| Chile | 1972 | | Oman | 1974 |
| China | 1973 | | Pakistan | 1958 |
| Colombia | 1974 | | Palau
| 2011 |
| Comoros | 2001 | | Panama | 1958 |
| Congo | 1975 | | Papua New Guinea | 1976 |
| Cook Islands | 2008 | | Paraguay | 1993 |
| Costa Rica | 1981 | | Peru | 1968 |
| Côte d'Ivoire | 1960 | | Philippines | 1964 |
| Croatia | 1992 | | Poland | 1960 |
| Cuba | 1966 | | Portugal | 1976 |
| Cyprus | 1973 | | Qatar | 1977 |
| Czechia | 1993 | | Republic of Korea | 1962 |
| Democratic People's Republic of Korea | 1986 | | Republic of Moldova | 2001 |
| Democratic Republic of the Congo | 1973 | | Romania | 1965 |
| Denmark | 1959 | | Russian Federation | 1958 |
| Djibouti | 1979 | | Saint Kitts and Nevis | 2001 |
| Dominica | 1979 | | Saint Lucia | 1980 |
| Dominican Republic | 1953 | | Saint Vincent and the Grenadines | 1981 |
| Ecuador | 1956 | | Samoa | 1996 |
| Egypt | 1958 | | San Marino | 2002 |
| El Salvador | 1981 | | Sao Tome and Principe | 1990 |
| Equatorial Guinea | 1972 | | Saudi Arabia | 1969 |
| Eritrea | 1993 | | Senegal | 1960 |
| Estonia | 1992 | | Serbia | 2000 |
| Ethiopia | 1975 | | Seychelles | 1978 |
| Fiji | 1983 | | Sierra Leone | 1973 |
| Finland | 1959 | | Singapore | 1966 |
| France | 1952 | | Slovakia | 1993 |
| Gabon | 1976 | | Slovenia | 1993 |
| Gambia | 1979 | | Solomon Islands | 1988 |
| Georgia | 1993 | | Somalia | 1978 |
| Germany | 1959 | | South Africa | 1995 |
| Ghana | 1959 | | Spain | 1962 |
| Greece | 1958 | | Sri Lanka | 1972 |
| Grenada | 1998 | | Sudan | 1974 |
| Guatemala | 1983 | | Suriname | 1976 |
| Guinea | 1975 | | Sweden | 1959 |
| Guinea-Bissau | 1977 | | Switzerland | 1955 |
| Guyana | 1980 | | Syrian Arab Republic | 1963 |
| Haiti | 1953 | | Thailand | 1973 |
| Honduras | 1954 | | Timor-Leste | 2005 |
| Hungary | 1970 | | Togo | 1983 |
| Iceland | 1960 | | Tonga | 2000 |
| India | 1959 | | Trinidad and Tobago | 1965 |
| Indonesia | 1961 | | Tunisia | 1963 |
| Iran (Islamic Republic of) | 1958 | | Turkey | 1958 |
| Iraq | 1973 | | Turkmenistan | 1993 |
| Ireland | 1951 | | Tuvalu | 2004 |
| Israel | 1952 | | Uganda | 2009 |
| Italy | 1957 | | Ukraine | 1994 |
| Jamaica | 1976 | | United Arab Emirates | 1980 |
| Japan | 1958 | | United Kingdom of Great Britain and Northern Ireland | 1949 |
| Jordan | 1973 | | United Republic of Tanzania | 1974 |
| Kazakhstan | 1994 | | United States of America | 1950 |
| Kenya | 1973 | | Uruguay | 1968 |
| Kiribati | 2003 | | Vanuatu | 1986 |
| Kuwait | 1960 | | Venezuela (Bolivarian Republic of) | 1975 |
| Latvia | 1993 | | Viet Nam | 1984 |
| Lebanon | 1966 | | Yemen | 1979 |
| Liberia | 1959 | | Zambia | 2014 |
| Libya | 1970 | | Zimbabwe | 2005
|
Associate Members:
| Faroes | 2002 |
Hong Kong, China
| 1967 |
| Macao, China | 1990
|