| SAARC | South Asian Association for Regional Cooperation | |
| SAC | Space Application Centre | |
| SAFTA |  South Asian Free Trade Agreement | |
| SAI | Sports Authority of India | |
| SAIL | Steel Authority of India Limited | |
| SAPTA | South Asian Preferential Trade Arrangement | |
| SARS | Severe Acute Respiratory Syndrome | |
| SC | Security Council/Supreme Court | |
| SCI | Shipping Corporation of India | |
| SCOPE | Standing Conference of Public Enterprises | |
| SCRA | Special Class Railway Apprentice | |
| SCSI | Small Computer Systems Interface | |
| SDR | Special Drawing Rights | |
| SEBI | Securities and Exchange Board of India | |
| SENSEX | Sensitivity Index (of Share Price) | |
| SEZ | Special Economic Zone | |
| SGPC | Siromani Gurudwara Prabandak Committee | |
| SHAR | Shri Harikota Range | |
| SIM | Subscriber Information Module | |
| SIS | Secret Intelligence Service (U.K) | |
| SITA | Suppression of Immoral Traffic in Women and Girls Act | |
| SlDBI | Small Industries Development Bank of India | |
| SLV | Satellite Launch Vehicle | |
| SMS | Short Message Service | |
| SMTP | Simple Mail Transfer Protocol | |
| SPCA | Society for the Prevention of Cruelty of Animals | |
| SPIC MACAY | Society for the Promotion of Indian Classical music and culture | |
| SRS |  Sample Registration System | |
| STARS | Satellite Tracking and Ranging Station | |
| STD | Subscriber Trunk Dialling; Sexually Transmitted Diseases | |
| STPI | Software Technology Parks of India | |
| SWAPO | South West African People's Organisation | |
| TA | Traveling Allowance/Territorial Army | |
| TADA | Terrorist and Disruptive Activities (Prevention) Act | |
| TC | Transfer Certificate, Trusteeship Council | |
| TCP | Transfer Call Protocol<br> Transmission Control Protocol | |
| TELCO | Tata Engineering and Locomotive Company | |
| TELEX | Tele-printer Exchange | |
| TERCOM | Terrain Contour Matching | |
| TFT | Thin-Film Transistor | |
| TIFR | Tata Institute of Fundamental Research | |
| TISCO | Tata Iron and Steel Company | |
| TNT | Tri-nitro-toluene | |
| TOEFL | Test of English as a Foreign Language | |
| TRAI | Telecom Regulatory Authority of India | |
| TRIPS | Trade Related Intellectual Property Rights | |
| TTE | Traveling Ticket Examiner | |
| TTFI | Table Tennis Federation of India | |
| TWA | Trans World Airlines (USA) | |