Dendrite growth of silicon from the undercooled melt of Si-45mass%Ni alloy was investigated. The dendrite growing along the melt surface was in-situ observed. By changing the cooling rate of the samples, the undercooling was varied from 6.7 to 18.8 K, and the growth velocity of dendrites was measured for different undercooling conditions. Both rod-and wedge-type dendrites grew in a sample, and the growth velocity of the former was slightly larger than that of the latter. Phase-field simulations were carried out in order to estimate the dendrite growth velocity at small undercooling. As the simulations at the undercooling corresponding to experiments were difficult because of the limitation of computational time, the extrapolated values of simulation results were compared with experiments, and both were in good agreement.