Several guano deposits found in the passages of Huda lui Papară cave (Trascău Mts, Romania) have been sampled to elucidate their mineralogical composition. The samples were studied by means of X-ray diffractometry (XRD), environmental scanning electron microscopy (ESEM) and energy dispersive X-ray analysis (EDS). Four phosphate minerals, belonging to three different types of deposits, have been identified in the samples: hydroxylapatite, ardealite, brushite and taranakite, associated with gypsum, calcite, and minerals of detrital origin (kaolinite, vermiculite, muscovite) and quartz. The phosphate minerals resulted from the interaction of acid solutions derived from the guano deposits with the limestones, calcite speleothems and/or detrital sediments in various conditions of pH and relative humidity.