When Kawasaki introduced the ZX-6R in 1995, it was the industry's first middleweight sport bike with an aluminum frame. It had a dry weight of 401.2 lb (182.0 kg), wet weight of 454 lb (206 kg), and was capable of accelerating 0-60 mph (97 km/h) in only 3.6 seconds.
With competition from Honda's CBR600F4i, Suzuki's GSX-R600, and Yamaha's YZF-R6 getting more aggressive, Kawasaki decided to make an unusual move for the 2002 model year. They increased the capacity of the traditional 600 cc (37 cu in) motor to 636 cc (38.8 cu in).
2002 Model
2003年改进油喷引擎，四缸前刹车，改进前避震。
2003 brought many new changes to the ZX-6R, or ZX636 as it is often referred. The engine was now fuel injected and engine speed was raised around 500 rpm which resulted in a slight gain in power. Radial-mounted 4-piston brakes replaced the previous 6-piston brakes and the front forks were now inverted.
In 2005, Kawasaki again revamped the ZX-6R. Engine speed increased again by 1,000 rpm resulting in 105 hp (78 kW) at 12,250 rpm. The frame and swingarm were updated, but the main changes from its predecessor lay in the design. The aluminum frame was now painted flat black, fairings were more round, and integrated turn signals were used (euro model). The exhaust was now centrically under the seat (a configuration commonly referred to as an undertail exhaust).
After four years of offering their 636 cc ZX-6R for street use, Kawasaki offers ZX-6R for 2007 with displaces of 599cc. Previous years of the ZX-6R's engines were all built from the same basic design, but the all-new engine for 2007 was redesigned from the crankcase up. In following with what their competitors had already been doing, Kawasaki's new engine features a stacked gear arrangement in which the crankshaft, primary drive and countershaft are placed in a triangular format for a shorter, more compact powerplant. It's now about 40 mm smaller in both length and width, said to yield greater cornering clearance.
2007 Model
忍者系列第四代（2009）
终于轮到我日思夜想的梦中情车出场了。2008年10月川崎重工推出第四代2009款Ninja ZX-6R，继2007年回归600cc引擎行列后，忍者再一次大回归。排气管重新回到了右侧，据说这样降低了整体重心，提高过弯灵活性，同时减轻了整体重量。（你早干什么去了嘛-____-|||）此外采用了新的前避震（Showa’s Big Piston Front fork technology），不过看不懂好在哪里嘿……
