Abstract: Fruits and leaves of Newhall navel orange（Citrus sinensis Osbeck‘Newhall’）and Cara Cara navel orange（Citrus sinensis Osbeck‘Cara Cara’）on trifoliate orange [Poncirus trifoliata（L.）Raf.] rootstocks from both normal and peel pitting orchards were used to study comparatively the fruit peel thickness，peel albedo microstructures，leaf and peel macroelement（N，P，K，Ca，Mg，S）content in relation to peel pitting at different stages after full bloom. The results showed that there was no significant correlation between fruit peel thickness and fruit peel pitting occurrence. Peel thickness decreased from 80 d to 140 d after full bloom，and peel pitting was related to the rate of decrease in peel thickness. Crevices or small pores began appearing in peel albedo of both Newhall and Cara Cara fruits from peel-pitting orchards 80 d after full bloom and expanded to sizes visible to the naked eyes in peel cross-sections 140 d after full bloom，and peel pitting symptom could be seen on fruit surface in this stage. Torn or shrunk cells were found in side of the crevices and pores. Ca content was significantly lower in peels of pitting fruits than in those of normal fruits 80，140 and 217 days after full bloom while the content of N，P，K，Mg and S did not show significant differences. Ca content in leaves of fruit pitting trees was also significantly lower in comparison with normal trees，but S content was significantly higher in leaves from orchards with pitting fruits. Leaf N，P，K and Mg content had no obvious difference between orchards of normal and pitting fruits. It was suggested that Ca deficiency was related to fruit peel pitting.

Key words: navel orange, fruit peel pitting, anatomy, macroelement, Ca