土霉素 Oxytetracycline也称为“地霉素”或“氧四环素”，是第二个被发现的广谱抗菌的四环素类抗生素。

土霉素是由Finlay等人在辉瑞实验室附近分离到的链霉菌Streptomyces rimosus中发现的。1953年生物化学家Robert B Woodward解析出土霉素的结构，使得辉瑞大规模生产土霉素成为可能，并用商品名Terramycin开始大量销售。Woodward的这一大发现是四环素类抗生素史上的重要发现，这一发现为土霉素的衍生物强力霉素的发现铺平了道路。

Oxytetracycline was the second of the broad-spectrum tetracycline group of antibiotics to be discovered.

Oxytetracycline works by interfering with the ability of bacteria to produce essential proteins. Without these proteins, the bacteria cannot grow, multiply and increase in numbers. Oxytetracycline therefore stops the spread of the infection and the remaining bacteria are killed by the immune system or eventually die.