Abstract A fiber sensor based on core-offset singlemode–multimode–singlemode (SMS) interferometer for simultaneous measurement of temperature and liquid level is proposed. The sensor is fabricated by a SMS interferometer spliced with a single mode fiber (SMF) in core-offset way. Since the cladding mode of SMF is excited in the core-offset SMS, two different kinds of interference dips which are formed by the SMF and the SMS interferometer respectively are obtained. Using the difference sensitivities to the two parameters of the selected dips, temperature and liquid level can be measured simultaneously. The chosen interference dips are at 1529.632nm and 1553.18nm. Experiments indicate that the dip at 1529.626nm is insensitive to liquid level, the temperature sensitivity is 0.064nm/°C. The temperature sensitivity of the dip at 1553.18nm is 0.082nm/°C. The temperature measurement precision is 0.001nm/°C. When the liquid is water (n=1.33), the sensitivity of the liquid level is 0.140nm/mm. When the liquid is sodium chloride solution (n=1.38), the sensitivity of the liquid level is 0.290nm/mm. The liquid level measurement precision is 0.001nm/mm. The interferometer also can be applied in other sensing fields.