PURPOSE: To provide the treating agent for object surfaces which is safe and clean and does not pollute environment and the method for treatment of this agent.

CONSTITUTION: The chlorella-dispersed treating agent of pH8.5 to 9.5 is prepd. by filtering a soln. formed by culturing living bacteria of the chlorella in natural mineral water without using chemicals at all, then diluting the chlorella satd. soln. 3 to 5 times with refined water and subjecting the soln. to photosynthesis under solar rays. The surface treatment of precision metallic parts and surface treatment of glass and marble, surface treatment of buildings, i.e., windows and aluminum sashes and further, cutting and polishing of metals are executed by spraying this treating agent or immersing the objects therein. Consequently, a rust preventive effect, effect of preventing oil film formation and dust pickup, lubricating effect and cleaning effect are obtd. Moreover, this treating agent is composed of the chlorella which is safe and harmless natural plants, such as algae, and therefore, the treating agent is safe and clean for operators and does not pollute environment at all even if the treating agent is discarded as it is.