We demonstrate, for the first time to the best of our knowledge, four wave mixing (FWM) process in a 900 nm wavelength region. A 54 m highly nonlinear photonic crystal fiber (HN-PCF) is used as nonlinear medium, and continuous wave laser diodes at near 975 nm are selected as pump sources. By simultaneously injecting two pump sources into the HN-PCF, FWM is observed with wavelength spacing of 0.4 nm and 2 nm, respectively. Compared with FWM in conventional highly nonlinear fibers, HN-PCF one possesses much higher conversion efficiency. These FWMs introduce an opportunity to extend the wavelength coverage of fiber lasers and amplifiers in 900 nm waveband, and also indicate that HN-PCFs can have great potential for FWM applications towards short wavelength regions.