OBJECTIVE: To analyze the effect of Pilates principles on the EMG activity of abdominal and paraspinal muscles on stable and unstable surfaces. METHODS: Surface EMG data about the rectus abdominis (RA), iliocostalis (IL) and lumbar multifidus (MU) of 19 participants were collected while performing three repetitions of a crunch exercise in the following conditions: 1) with no Pilates technique and stable surface (nP + S); 2) with no Pilates technique and unstable surface (nP + U); 3) with Pilates technique and stable surface (P + S); 4) with Pilates and unstable surface (P + U). The EMG Fanalysis was conducted using a custom-made Matlab(®) 10. RESULTS: There was no condition effect in the RA iEMG with stable and unstable surfaces (F(1,290) = 0 p = 0.98) and with and without principles (F(1,290) = 1.2 p = 0.27). IL iEMG was higher for the stable surface condition (F(1,290) = 32.3 p < 0.001) with Pilates principles (F(1,290) = 21.9 p < 0.001). The MU iEMG was higher for the stable surface condition with and without Pilates principles (F(1,290) = 84.9 p < 0.001).