Urban cats live in cities like humans and humans affect their life intentionally or unintentionally. Waste production is only one of the human effects on the urban cat ecosystem. The waste produced by human supply some of the food needed by urban cats. This descriptive - estimation research is the first study in the world to measure the cats’ weight to investigate the effect of the increase or decrease in urban wastes on physical status of cats. In the first phase of the research (Spring 2016-Winter 2017) in Tehran, we found that the average volume of the collected wastes had increased by 14% and the average weight of cats in the mentioned period had increased 1%. The 9.5% decrease in the waste volume in Autumn 2016 had led to the decrease in the average weight of cats in Winter 2017. The male cats were more affected by the decrease in waste volume.