Photocatalysis is a well-established and green technique for degradation of antibiotics in wastewater. Hydroxyapatite (HAp) has excellent biocompatibility, biological activity, non-toxicity and low cost, and has many applications in biomaterials. Recently, HAp has been reported as an inexpensive green photocatalyst for cleaning some drug contaminations. However, its photocatalytic performance and chemical stability are far from practical applications. In this research, a series of porous hollow hydroxyapatite (HAp) microspheres decorated with small amounts of ultrathin graphitic carbon nitride (g-C3N4) were firstly and successfully fabricated by a facile hydrothermal procedure. The experimental results show that as-prepared g-C3N4/HAp photocatalysts exhibited evidently enhancement on the photocatalytic activities for the degradation of tetracycline (TC), compared with the corresponding ultrathin g-C3N4 and porous hollow HAp microspheres. Notably, g-C3N4 (1.5 wt.%)/HAp composite displayed a net high photocatalytic activity for TC degradation (almost 100% within 15 min). Moreover, the as-prepared g-C3N4 (1.5 wt.%)/HAp exhibited a good stability in the cyclic runs for the photocatalytic degradation of TC, demonstrating its promising potential as an efficient photocatalyst. An optimum decorating amount of ultrathin g-C3N4 onto porous hollow HAp microspheres favors an effective separation of photogenerated electron-hole pairs, which can be responsible for the enhanced photocatalytic performance. In addition, the photocatalytic degradation mechanism for TC was proposed. This fundamental research will provide a promising strategy for the development of highly efficient and compatible photocatalysts with many applications.