This study aims at clarifying the effects of delamination on fretting wear behaviors of plasma-sprayed hydroxyapatite coating. Plasma-sprayed hydroxyapatite (HAp) coating has been widely used as a bond between human bone with artificial metallic implants in order to smoothly transmit loads by gaits. However, HAp coating is susceptible to be failed due to brittle fracture, fatigue cracks, wears by fretting or corrosion etc. Wear particles made by fretting are concerned for activating inflammatory reactions at surrounding organs, which lead to loosening of implants or subsequent failures. Delamination in interfaces of HAp coating can accelerate the wear behaviors in fretting fatigue. Moreover, adhesive conditions between human bone with artificial implants can affect such the delamination / wear behaviors of HAp coating. Adhered contact surfaces between human bone with artificial implants are practically believed to suppress such wear behaviors. However, no experimental study to observe the behaviors has been conducted. An in-situ observation system of fretting fatigue was facilitated. The in-situ observations revealed that higher stress amplitudes and lower contact pressures promoted growth rates of delamination. Furthermore, delamination between HAp coating with metal substrates could accelerate the wear amounts from both the artificial human bone and HAp coatings. Adhered contact conditions between contact pads with coated substrates demonstrated lower delamination growth rates in HAp coating. Even in the cases of adhered contacts conditions, delaminaion continued propagations, which indicated that wear behaviors would occur once delamination reached a certain length. Finite element analyses also revealed that delamiantion length in HAp coating could mainly promote wear behaviors of HAp coating.