The tissue optical clearing technique shows great potential in optical diagnosis and therapy. However, short-term and long-term effects of optical clearing agents on blood vessels, which are relevant to the safety of clinical applications, have not been clarified. We used laser speckle contrast imaging to monitor the changes in blood vessels in chick chorioallantoic membrane (CAM) after application of glycerol or glucose. The changes in morphology of vessels and blood flow velocity were measured. Long-term effects on blood vessels were investigated by observing the function and the development of blood vessels. The results show that glycerol reduces the local blood flow velocity and constricts and even blocks vessels quickly. At 2 days, the blood flow velocity is recovered to different extents, and new blood vessels develop but are fewer in number. Glucose induces slow changes in blood flow or vessels. However, most blood vessels are blocked, and no new blood vessel develops at 2 days. The effects depend on the dosage of agents, including volume and concentration, and decrease with the dosage of agents. Therefore, short-term effects of glucose on blood vessels are slighter than those of glycerol, but long-term effects of glucose are greater.