An in-fiber Mach-Zehnder interferometer is proposed for the discrimination of strain and temperature. The sensor is based on two cascaded standard single mode fibers using three peanut tapers fabricated by simple splicing. The cascaded structure excites more frequency components, which induce four sets of interference dips in the transmission spectrum. One set of the spectrum dips have different sensitivities to temperature and strain from those of the other three. The sensor can discriminate strain and temperature by monitoring the wavelength shifts of two spectrum dips. Repeated experiments are taken both for strain and temperature increasing and decreasing scenarios. Experimental results show that Dip 1 has an average strain sensitivity of -0.911 pm/με and an average temperature sensitivity of 49.98 pm/℃. The strain sensitivity for Dip 2 is negligible and its average temperature sensitivity is 60.52 pm/℃ The strain and temperature resolutions are ±3.82 με and ±0.33 ℃.