To the third declension belongs masculine nouns which ends with -us in singular nominative and few old feminine nouns: dzirnus, pelus, ragus. The case endings for third declension nouns are given in following table:
| Nom. | Gen. | Dat. | Acc. | Loc. | Voc. | |
| sing. | -us, | -us | -um | -u | -û | -us |
| plur. | -i | -u | -iem | -us | -os | -i |
| Nominative | liet-us | liet-i |
| Genitive | liet-us | liet-u |
| Dative | liet-um | liet-iem |
| Accusative | liet-u | liet-us |
| Locative | liet-û | liet-os |
| Vocative | liet-us | liet-i |