摩托化自行车或附发动机自行车是有动力的自行车，现在的摩托车即是从发动机自行车演变而来，摩托化自行车的发动机种类非常多，从二冲程引擎、四冲程引擎、电动机甚至蒸汽机的都有。电动自行车也是一种摩托化自行车。

最早的摩托化自行车装有发动机来帮助踩踏，那时汽油引擎与传动设计还在萌芽的阶段，其功率重量比很低，所以这种双重动力系统在此时特别有优势。随着技术的改进，踏板推进被二冲程或四冲程的汽油引擎取代，不过在一些汽机车与燃料都还是很贵的国家，摩托化自行车仍然很盛行。

现在的摩托化自行车有多种种类：

A pedelec (from pedal electric cycle) is a bicycle where the rider's pedalling is assisted by a small electric motor; thus they are a type of low-powered e-bike. However, unlike some other types of e-bikes, pedelecs are classified as conventional bicycles in many countries by road authorities rather than as a type of electric moped. Pedelecs include an electronic controller which cuts power to the motor when the rider is not pedalling or when a certain speed – usually 25 km/h (15 MPH) – has been reached. Pedelecs are useful for people who ride in hilly areas or in strong headwinds. A pedelec can be any type of bicycle, but a pedelec city bike is very common. Ordinary conventional bicycles can be converted to pedelecs with the addition of the necessary parts, i.e. motor, battery etc.