This book provides a brief knowledge about synthesis and medicinal importance of benzimidazolyl derivatives and pyrazolines. Chapter one of this book incorporates introduction and importance of benzimidazolyl chalcones and pyrazolines. Chapter two includes account on synthesis of pyrazoline using microwave-assisted and conventional methods. Synthesis of 3-benzimidazolyl-5-aryl-2-pyrazoline-1-carboxaldehydes and characterization of synthesized compounds is given in chapter three. Chapter four deal with biological activities of benzimidazolyl derivatives. Chapter five includes study of antimicrobial (antibacterial and antifungal) activities of 3-benzimidazolyl-5-aryl-2- pyrazoline-1-carboxaldehydes.