In urban ecosystems, helminthiases transmitted through the soil remain a serious epidemiological problem. The most common and dangerous among them is the larval toxocarosis caused by two species of Toxocara genus (T. canis and T. cati), parasitizing in adult stage respectively in dogs and cats. The issues of environmental contamination by infective agents and its sanitary evaluation are related to the elucidation of the stability (survival) of infective helminthes eggs to the effects of natural and anthropogenic factors. Relative humidity, temperature, oxygen content, and soil type and depth are the main factors determining the rate of insemination and survival of toxocara eggs in the soil. When comparing the development and survival rates of toxocara eggs in different types of soil substrates (low-lying peat, typical Chernozems (black earth), soil-garden soil, soil mixture for lawns, sand), it was found that the most favorable environment for them was a soil mixture for lawns (survival around 70%). As the upper limit of temperature for the development of toxocara eggs was 40 °C, optimal ranges of the above factors are established at 51–59% for soil moisture, 82–93% for relative air humidity. When the moisture values deviated from the optimal values, the development of T. canis eggs slowed down, also the number of deaths increased.