The present disclosure provides an atomizer and an electronic cigarette using same. The atomizer comprises a core assembly. The core assembly comprises an airflow shell, an atomizing seat partially accommodated in the airflow shell, and an oil-guiding seat connected with a part of the atomizing seat uncovered by the airflow shell. At least one air-inlet passage is formed between an inner wall of the airflow shell and an outer wall of the he atomizing seat. An atomizing chamber is defined inside the atomizing seat, and an oil-guiding chamber is defined inside the atomizing seat. The air-inlet passage and the oil-guiding chamber both communicate with the atomizing chamber. The atomizer of the present disclosure adopts a top air-inlet structure in order to solve the question of bottom oil leakage in the traditional electronic cigarette and has a better atomizing performance.