This paper presents a method to design Raman amplifiers using a multi-objective particle swarm optimizer. The goal is to define the number of pump lasers and their wavelengths and powers in order to maximize both the average on-off gain and the flatness of the gain. The multi-objective optimizer aims to generate non-dominated solutions considering the average on-off gain, the number of used pump lasers and the gain ripple over the transmission bandwidth. The experimental results showed that our proposal is robust and can generate Pareto Fronts which are useful to design real Raman amplifiers. From these results, we observed that the designer can easily determine the minimum number of pump lasers to build the amplifier properly. As an example, we designed an amplifier with ripple and average on-off gain equal to 0.2 dB and 20 dB, respectively, for the case where 40 signal channels are amplified with total pump power equal to 1.5 W.