Management is considered to be science because : 

Systematic Body of Knowledge : Management is a systematized body of knowledge based on cause and effect relationship e.g., genetic principle derived by Darwin. Like all other organized activity, management has its own vocabulary of terms through which managers communicate with each other.

Observations and Experiments: The principles of management have also been developed over a period of time, on the basis of experimentation and observation. Management experts and practitioners have developed the knowledge after careful analysis, inquiry and experience. Management deals with human beings and human behavior which cannot be scientifically predicted.

Cause and Effect Relationship : Management Principles builds the cause and effect relationship between various factors. For example, dual subordination leads to confusion.

Universal Validity of Principles : The principles of science are universally applicable i.e.. these principles hold time under each and every situation. These principles have universal validity. These principles have to be modified according to the situation.