The Megacystium sinensis was collected as a new genera and new species of Lecithodendriidae from a monkey (Macaca mulatta) in Guangxi, China. This paper reported further observation by histomorphological method of this new species of Lecithodendriidae. The excretory vesicle was very large. The wall of excretory vesicle was single layer columnar epithelium. Two excretory tubes, 35-37 μm long, V-shaped, existed on the top of excretory vesicle. Ovary, Mehlis gland, Vitellarium linked with one side of the Fallopian tube, while uterus linked with the other side of the Fallopian. Vaginal opening was observed on reproductive hole, while other side of vagina was connected to metraterm. Vagina wall was thick muscle layer. In vagina there were some eggs. Cirrus poach was large and oval in shape, and opened to the genital pore, ending at post dorsal acetabulum. Cirrus poach was filled with a bundle of muscle fibers. Cirrus poach had an S-curved ejaculatory duct, U-shaped seminal vesicle, and vas deferens. In mucosal surface of middle ejaculatory duct there was distribution of bundles of muscle fiber. Vas deferens and seminal vesicle were located at the end cirrus poach.