What is study of reptiles and amphibians called as ?

Herpetology

The answer is Herpetology.

Herpetology is the scientific study of amphibians and reptiles. It encompasses all aspects of their biology, including their evolution, anatomy, physiology, behavior, ecology, and conservation. Herpetology is a branch of zoology, the scientific study of animals.

Histology is the study of tissues. Entomology is the study of insects. Gerontology is the study of aging.